Aquarium Supplies, Products, and Cultures

Almost everybody who has ever kept fish remembers the first tank: a glass box on a countertop, a little light humming, bright fish drifting through green plants, and the calm that settles over a room when you sit and watch water. It is one of the most relaxing things a family can keep. It is also the hobby where the biggest cause of dead beginner fish has nothing to do with the fish. It is an invisible, natural process called the nitrogen cycle (the way helpful bacteria turn toxic fish waste into much safer substances), and most people set up a first tank without hearing about it. They bring the fish home the same afternoon, and within a week or two the fish are gone and nobody knows why. This guide is written so that does not happen to you. We will set up a tank, grow the beneficial bacteria that keep it safe before any fish arrive, choose fish that suit one another, feed them well, and handle common problems calmly. Our approach is the one we bring to everything at Walnut Creek Supply: natural-first, low-stress, and stability over perfection. A boringly steady tank is a beautiful tank.

Quick Start: Your First 48 Hours

These ten steps take you from an empty box to a tank that is quietly growing its own bacteria. Notice what is missing: no fish go in during the first 48 hours. The first stretch of a new tank's life is for the water, not the fish. Fish come home when your test kit says the tank is ready, usually three to six weeks from now. That wait is the single best investment you can make.

1. Pick the spot and set up a stand that can carry the weight. Water weighs about 8.3 pounds per gallon, so a 20 gallon tank holds roughly 170 pounds of water before you add glass, gravel and stand. Choose a level, sturdy stand rated for the tank (never a bookshelf or a dresser), away from direct sunlight, vents and busy doorways, with room behind for cords and a hand to reach the filter.
2. Rinse everything with plain water, never soap. Soap and detergent leave films that harm fish gills. Rinse the tank, substrate, décor and filter parts; gravel and sand are done when the rinse water runs mostly clear. Some dust will remain, and that is fine.
3. Place the substrate and hardscape. Add substrate (see Substrate, Décor & Plants), sloping it slightly higher at the back. Position rocks, driftwood and caves now, while the tank is empty, and set heavy pieces on the glass floor so a digging fish cannot undermine them.
4. Install the filter and heater, but do not plug them in yet. Choose a filter rated for your tank volume and a heater sized to the tank (roughly 3–5 watts per gallon in a typical room). Place the heater where water flows past it. Never run a heater out of water.
5. Fill the tank with water treated with a dechlorinator. A dechlorinator (water conditioner) is a liquid that neutralizes the chlorine and chloramine municipal water systems add, which would otherwise burn fish gills and kill beneficial bacteria. Dose it for the full tank volume, then fill, pouring onto a plate or bowl so you do not blast a crater into your layout.
6. Plug in the filter and heater and set the temperature. Set the heater to 78°F for a tropical community tank and confirm with a separate thermometer; the heater dial is a suggestion, not a measurement. (Goldfish are the exception, since they want cool water. See Meet Your Freshwater Aquarium.) Confirm the filter is moving water and the surface is gently rippling.
7. Plant the tank. A few easy low-light plants (java fern, anubias, vallisneria, cryptocoryne) make the tank steadier, give fish cover, and take up waste nitrogen. Tie java fern and anubias to wood or rock; never bury their thick horizontal stems (rhizomes), or they rot.
8. Put the light on a timer. Run it 6–8 hours a day. More than that and algae thrives long before your plants do. A plain outlet timer costs a few dollars and removes the daily decision.
9. Start the cycle. Test your water first and record a baseline for ammonia (the toxic waste fish produce), nitrite (a second toxic by-product) and nitrate (the far milder end product), plus pH. Readings are in ppm (parts per million). Then add an ammonia source: pure household ammonia (plain and clear, with no scents, dyes or added detergent; shake the bottle, and if it foams, it is the wrong product) until your kit reads about 2 ppm. A bottled bacteria starter is optional. Write each day's numbers on a calendar near the tank. The full process is in The Nitrogen Cycle.
10. Line up your help before you need it. Buy a liquid test kit for ammonia, nitrite, nitrate and pH. Write down your local fish shop's number. Decide how you will quarantine new fish (keep them in a separate small tank for a few weeks before they join the others). Keep a clean bucket for the aquarium only, never for cleaning chemicals, and a gravel vacuum beside it.

First-Time Starter Bundle

What needs to be in the house before the first fish, and what to look for in each category.

Essentials

• A tank sized for a community, with a lid — a 20 gallon long or a 29 gallon is the best beginner minimum. A "long" tank has more surface area and floor space than a "high" tank of the same volume. A tight lid or hood is not optional: many fish jump.
• A rated stand built for the weight — level, solid, and wide enough to support the glass edges.
• A filter rated for the tank volume — hang-on-back, canister or sponge. A sponge filter driven by an air pump is gentle, cheap, and especially good for bettas and shrimp.
• Filter media for biological filtration — ceramic rings or bio-sponge with plenty of surface area. This is where the bacteria live; mechanical floss only catches debris.
• An adjustable heater with a separate thermometer — correctly sized, with a guard if needed. A thermometer at the opposite end of the tank from the heater tells you the truth.
• A water conditioner (dechlorinator) — one that neutralizes both chlorine and chloramine. Keep a bottle at every water change.
• A liquid test kit for ammonia, nitrite, nitrate and pH — more accurate and cheaper per test than strips. Strips are a handy convenience, never a diagnosis.
• A gravel vacuum and a dedicated bucket for weekly water changes.
• An LED light on an outlet timer.
• A fine-mesh net — for moving fish gently when you must. Keep a second one for the quarantine tank so nothing travels between tanks on a shared net.

Ready to set up? Browse the essentials in our collections: Aquarium Filters, Pumps & Media, Aquarium Lighting, Aquarium Substrate and Aquarium Chems, Conditioners, Cultures.

Enrichment

• Easy low-light live plants — java fern, anubias, vallisneria, cryptocoryne and floating plants. They take up nitrate, shade the water, and give fish places to feel safe.
• Driftwood and smooth rock — aquarium-safe wood soaked until it sinks, and smooth stones that do not change your water chemistry. Wood adds harmless tannins that tint the water tea-colored.
• Caves and hiding places — ceramic caves, tubes or a tangle of roots. A fish with somewhere to hide is a fish that comes out and explores.
• A hospital or quarantine tank, even a small one — a plain 5–10 gallon tank with a sponge filter and heater pays for itself the first time you need it.

Enrichment, one click away. Shop Aquarium Decorations and Accessories, Aquarium Live Plants & More and Aquascape Kits & Hardscape.

Meet Your Freshwater Aquarium

A healthy freshwater aquarium is a small, living ecosystem in a glass box, not a decoration with fish in it. Colonies of invisible bacteria live in the filter and on every surface, quietly turning fish waste into something safer. Plants take up what is left. Fish eat, breathe and live above all of it. When the balance is right, the water is clear, the fish are active and colorful, the plants slowly grow, and the tank looks after itself with about an hour of attention a week.

A healthy tank has ammonia and nitrite at 0 ppm, low and steady nitrate, a stable temperature, clear water with a faint earthy smell (never a foul one), fish that eat eagerly, swim in the open and show good color, and plants with new growth. A beginner should expect a few weeks of waiting at the start, a little weekly maintenance, some algae now and then, and the occasional loss. The goal is not perfection; it is a tank steady enough that problems are rare, small, and easy to catch.

Each group has its own habits. A short note on each:

Community fish. Tetras, rasboras, corydoras, livebearers (guppies, platies, mollies and swordtails, which bear live young) and danios are the classic beginner fish: small, colorful, peaceful in the right company, and happiest in groups. Keep schooling fish in groups of at least six; a lone neon tetra is a nervous neon tetra.

Bettas. A betta is a magnificent, intelligent little fish that learns the person who feeds it. Bettas are not "puddle fish" that thrive in vases or bowls; that is a sales myth. They come from warm, slow, vegetated waters and need at least 5 gallons, heated to 78–80°F, with a gentle filter and hiding places. Males fight to injury, so keep one betta per tank. Long fins and strong currents do not mix, so choose a filter with adjustable flow.

Goldfish. Goldfish are cool-water fish that grow big, live long, and make more waste than almost any other common pet fish. Fancy goldfish (round-bodied varieties like orandas, ranchus, fantails and ryukins) can live in a large aquarium: plan roughly 20 gallons for the first fish plus 10 for each additional, at 65–72°F, with strong filtration. Common and comet goldfish (the long-bodied, single-tailed kind sold as carnival or "feeder" fish) and koi grow far too large for any home aquarium and belong in ponds. None of these mix with a tropical tank.

Cichlids. Cichlids are a huge family of intelligent, often territorial fish. African cichlids from the Rift Valley lakes (Malawi and Tanganyika) like hard, alkaline water and are usually kept in species-matched, rock-heavy tanks of 55 gallons or more. South American cichlids such as angelfish, rams and severums prefer softer, slightly acidic water with plants and wood; angelfish need tall tanks, and large species like oscars need far bigger tanks than their store size suggests. Cichlids are rewarding but not ideal first fish: pick a species first, then build the tank around it.

Freshwater shrimp. Cherry shrimp (a bright red dwarf species) and crystal red shrimp (a striking red-and-white, pickier cousin) are fascinating to watch as they graze across plants and wood. They need very stable water with little nitrate, no copper, and no big predators. Cherry shrimp are the more forgiving of the two.

Nano tanks. A nano tank is anything under about 10 gallons. They are charming, but they are harder, not easier: a small volume of water changes quickly, and one overfeeding can swing the chemistry in hours. We recommend nanos for experienced keepers, a single betta, or a shrimp colony. If you are new to fish, buy the biggest tank your space and budget comfortably allow.

Planted tanks. A planted tank simply has enough live plants to shape the water. You do not need high-tech lights or injected carbon dioxide to begin; easy plants like java fern, anubias, vallisneria and cryptocorynes grow quietly under modest light and make a tank steadier and more beautiful. It is an excellent natural-first path.

What about saltwater, reef and ponds? Saltwater and reef aquariums need different equipment, chemistry and expertise, and have their own Walnut Creek Supply guide; start there once your freshwater tank is humming. A pond is an outdoor ecosystem that needs enough volume and depth to stay stable through summer heat and winter freeze, and it suits common goldfish and koi. It is a long-term landscaping project more than a pet purchase, and deserves its own research.

What surprises new owners

Most new keepers are surprised by three things. The first is the wait: nothing in the pet aisle prepares you to hear that the best thing to do with a new tank is leave it empty of fish for a month, but that month turns a glass box into a safe home. The second is how much easier bigger is: a 29 gallon is far more forgiving than a 5 gallon, because the same mistake dilutes in more water. The third is that "one inch of fish per gallon" is a myth. It ignores that a 10 inch goldfish makes far more waste than ten 1 inch tetras, that schooling fish need numbers, and that adult size and temperament matter more than store size. See Stocking & Compatibility.

Tank Setup & Layout

Choosing the tank size

Bigger is easier. This is the most useful sentence in the hobby. More water dilutes waste, holds its temperature, and changes chemistry slowly, which gives you time to notice a problem and fix it. For a beginner community we recommend a 20 gallon long or a 29 gallon as the minimum: a long footprint (floor area matters more than height), room for a school of small fish plus bottom dwellers, and a margin for error.

Placement, stand and lid

Pick the spot before you buy the tank, since once it is full it is not moving. The tank belongs on a level, rigid surface rated for the filled weight: a 29 gallon tank with water, substrate and décor can top 350 pounds. A purpose-built aquarium stand is safest. Check it with a bubble level, since an out-of-level tank stresses the glass seams, and follow the tank maker's guidance about any foam leveling mat.

Keep the tank out of direct sunlight (which fuels algae and swings the temperature), away from vents, drafty windows and exterior doors, and away from loudspeakers, since vibration startles fish. Plug into a ground-fault protected outlet and give every cord a drip loop (let it hang below the outlet before it climbs back up, so water runs off the loop and not into the socket).

A lid or hood is part of the tank. Many fish jump, including danios, hatchetfish, bettas and even some tetras and gouramis. A lid also keeps out dust and curious cats, slows evaporation, and holds heat. Leave a small gap for cords and air tubing.

Tank layout — a labeled map from back to front

A good layout mixes open swimming space, cover, and clear lines for maintenance. Sketched front-on as a labeled diagram, it runs like this, back to front.

Back wall: a dark or natural background on the outside of the back glass. At one back corner sit the filter intake and outflow, with the heater beside the outflow. Put the thermometer at the opposite end so you read the coolest spot.

Back third: tall plants such as vallisneria along the back and one end form a green backdrop, with taller wood or rockwork anchoring one side. Floating plants at the surface shade the water and give shy fish cover.

Midground: mid-height cryptocorynes and clusters of java fern and anubias attached to wood and rock. This is the cover zone, with one or two caves or hollows for bottom dwellers.

Open front third and center: keep this clear. It is the open swimming lane where schooling fish cruise, where you vacuum, and where food lands. Use smooth sand or gravel with a few low plants at the corners.

Surface: a gentle ripple where the filter outflow breaks the water, with a small air gap under the lid. Bettas and gouramis breathe surface air, so leave them a clear spot to reach it.

Lighting: on a timer above the lid, 6–8 hours a day.

Aim for planting and hardscape to fill roughly one third to one half of the footprint, leaving open water. Arrange rocks and wood in natural groupings, never with tight gaps: if a fish can fit its head in a gap, it can get trapped.

Substrate, Décor & Plants

Substrate

The material on the bottom of the tank holds bacteria, anchors plants, and shapes how bottom dwellers behave. Corydoras and loaches forage with sensitive barbels, so smooth sand or rounded gravel suits them far better than sharp gravel.

Aim for a depth of roughly 1.5–2 inches, a little deeper at the back. Too thin and plants will not root; very deep beds can develop pockets where debris goes sour.

Décor and hardscape

Choose rocks, wood and ornaments that are aquarium-safe with no sharp edges. Test a questionable rock by dripping white vinegar on it: if it fizzes, it contains carbonates that will raise pH and hardness over time, which suits African cichlids and few others. Aquarium driftwood should be soaked until it sinks, which may take days or weeks; it leaches harmless tannins that tint the water, and bettas and tetras like it.

Run a soft nylon stocking around every edge and opening of an ornament. If it snags, it can tear a fin. This matters most for long-finned bettas and fancy goldfish.

Plants

Live plants take up nitrate and ammonia, compete with algae for nutrients, oxygenate the water in daylight, and offer cover that lowers fish stress. Start with the forgiving ones.

Rinse every new plant gently before adding it; plants can carry snails, hitchhikers, and sometimes pesticides. Never release unwanted aquarium plants into ponds, streams or storm drains, because many are invasive. Bag them and put them in the trash, or dry them out and compost them.

Avoid outright

• Painted, glittery or coated gravel and ornaments that are not labeled aquarium-safe; the coating can flake or leach.
• Sharp, jagged or snaggy décor, including some cheap plastic plants with stiff edges, which tear fins.
• Untreated wood, rocks, shells or coral collected outdoors, which can carry parasites or chemicals and alter your water. Buy aquarium-labeled items.
• Limestone, marble, seashells and crushed coral in community or soft-water tanks, because they steadily raise hardness and pH.
• Metal objects that can rust, and anything touched by soap, polish or cleaning spray.
• Tight gaps or small tubes where a fish can wedge itself.
• Toys and ornaments not designed for water, which can leach chemicals.
• Bowls, vases and tiny globes with no filter, heater or swimming room. They are not suitable homes for any fish.

Water Parameters — The Numbers

You cannot see most of what keeps a fish healthy; you can only measure it. This is why a liquid test kit belongs next to the tank. Learn a few numbers, test regularly, and you will catch nearly every problem before the fish show it. The big idea is stability: water that is steadily "pretty good" beats water that is constantly fixed and re-fixed to chase a perfect number.

A few terms in plain language. Ammonia is the toxic waste fish release through their gills and droppings, and it is also released as uneaten food and plant matter rot. Nitrite is what the first group of bacteria turn ammonia into, and it is almost as toxic; it blocks the blood from carrying oxygen. Nitrate is what a second group turn nitrite into; it is far less toxic and builds up slowly until water changes and plants remove it. KH (carbonate hardness) measures the minerals that buffer pH and keep it from dropping suddenly. GH (general hardness) measures dissolved calcium and magnesium, which fish and shrimp use for bones, scales and shells. Your water utility's report usually lists both; well water should be tested directly.

Two reminders. First, a steady pH matters far more than a particular number: most community fish adapt to anything in the 6.5–7.8 range if you do not swing it quickly, so do not add "pH up" or "pH down" products to a new tank. Second, ammonia grows more dangerous as pH and temperature rise, so even a reading of 0.25 ppm deserves a water change and a second look.

The Nitrogen Cycle

The nitrogen cycle is the natural process that makes a closed tank of water safe to live in. It is the most important idea in this guide, and the one that most often goes unexplained at the point of sale. Here is the whole story in plain language.

Fish breathe, eat and excrete, and that produces ammonia, which is toxic; uneaten food and decaying plants add more. In a brand-new tank nothing deals with it, so it builds up. Over days, a first group of beneficial bacteria moves into the filter media and onto every surface and eats ammonia, producing nitrite, which is also toxic. Then a second group eats nitrite and produces nitrate, which is far less harmful and is removed by water changes and plants. Once both colonies are large enough for the waste in the tank, the tank is cycled: ammonia and nitrite read zero and nitrate is present. The colonies take time to grow because bacteria multiply slowly in a clean new tank with little to eat.

This is why a fish put into an uncycled tank often seems fine for several days and then dies. Ammonia and nitrite quietly climb until they burn the gills. The fish was never "sickly"; the tank was not ready. Hobbyists call it new tank syndrome.

Fishless cycling — the kindest way

Fishless cycling grows the bacteria with an ammonia source and no fish at risk. It is gentler and more controlled, and you can stock the tank properly when it is done.

1. Set up the tank completely: filter running, heater on, dechlorinated water, plants if you have them.
2. Add an ammonia source: pure household ammonia (see Quick Start) or a dedicated aquarium ammonia product, dosed to about 2 ppm. A slower, messier alternative is a pinch of fish food each day, left to rot.
3. Optionally add a bottled bacteria starter and, if you can, used filter media from a healthy established tank, the best shortcut available. Bottled bacteria can help, but they do not remove the need to test.
4. Test every day or two and write the numbers down. Ammonia slowly falls, nitrite appears and rises, then nitrite falls and nitrate appears.
5. Re-dose ammonia to 2 ppm whenever it reads near zero, to keep feeding the bacteria.
6. The tank is cycled when, 24 hours after dosing ammonia to 2 ppm, both ammonia and nitrite read 0 ppm and nitrate is present.
7. Do a large water change (about 50–80%, dechlorinated and temperature-matched) to bring nitrate below 20–40 ppm, then add your first fish within a day or two. If you must wait, keep dosing a little ammonia to keep the bacteria fed.

Fish-in cycling — the honest version

Sometimes people already have a fish and a new, uncycled tank: a gift, a rescue, a regretted impulse buy. Cycling with the fish in is possible, but it is harder on the fish. Use the hardiest fish you can, keep the number tiny, feed very lightly, and test ammonia and nitrite every day. Whenever either reads above 0.25 ppm, do a 30–50% water change with dechlorinated, temperature-matched water. Some conditioners also temporarily detoxify ammonia, which buys time. Expect weeks of daily vigilance, and add no more fish until readings stay at zero between water changes. If the choice is yours, cycle fishless.

Timeline

Every tank is different: warmth, source water, starter bacteria, seeded media and the ammonia dose all change the speed. Most tanks take three to six weeks; a few take two or eight. A typical fishless cycle looks like this.

Troubleshooting stalls

A cycle that seems to have stopped is usually fixable. Check these first.

• Cold water. Bacteria slow dramatically below about 70°F. Warm the tank to 78°F and wait.
• Chlorine or chloramine. Untreated tap water kills bacteria. Recheck your dechlorinator dose and always treat water for water changes and top-offs.
• pH or KH too low. Bacteria slow or stop when pH falls below about 6.5 or KH is near zero. Test both. A little crushed coral in the filter or a proper KH buffer can help; do it slowly and avoid big swings.
• Ammonia too high. Above about 5 ppm can stall the bacteria. If your test reads that high, do a water change and re-dose to 2 ppm.
• Cleaning the filter. Bacteria live in the filter media. Rinsing it in tap water or replacing all of it resets the clock. Never wash media under the tap; rinse gently in old tank water.
• Medications or cleaning products. Antibiotics and some treatments harm bacteria. Treat sick fish in a hospital tank, and keep soap, sprays and polish away from the aquarium.
• No ammonia source. If you stopped dosing, the bacteria have nothing to eat. Dose again.
• Nitrate stays at zero. Fast-growing plants may use nitrate as fast as it appears. If ammonia and nitrite both clear within 24 hours, you are cycled.
• Just waiting. Three to six weeks is normal; eight is not a failure.

A mini-cycle can follow a big addition of fish, a heavy overfeeding, or a filter cleaning: ammonia or nitrite pops up for a few days. Do a water change, feed less, and keep testing until it settles.

Diet & Nutrition

Feeding is where kindness most often goes wrong. A fish that begs is not a fish that is hungry; fish are opportunistic eaters and will eat far more than they should. Overfeeding is the second biggest killer of aquarium fish, right behind the nitrogen cycle. Extra food rots, spikes ammonia, fouls the substrate, and fuels algae and cloudy water. We hold fish food to the same standard as every pet food we sell: Clean Fuel, No Junk. Read the label. The first ingredient should be a recognizable whole food such as fish, krill, shrimp, spirulina or a named plant, not an unnamed meal or filler.

Feeding by fish type

Match the food to the mouth, the habits and the body shape. Surface feeders take floating flake. Mid-water fish take flake or micro-pellet. Bottom dwellers need food that sinks.

Schedule and quantity

Feed small amounts once or twice daily, only what the fish eat in about two minutes. Watch the first feedings closely; if food is still drifting or sitting on the bottom after two or three minutes, you fed too much. Skip one feeding a week as a "fasting day"; this helps digestion and keeps the water cleaner. A healthy adult fish can go a week without food with no harm, so a short trip does not need an automatic feeder or a neighbor stuffing the tank. For a longer trip, ask a trusted friend and give them pre-portioned packets, one per day, so a well-meaning "extra" does not become a disaster.

Variety matters. A staple flake or micro-pellet forms the base. Add frozen or live foods such as bloodworms, brine shrimp and daphnia several times a week for carnivores and omnivores; frozen is safer than live because it is less likely to carry disease. Offer blanched vegetables (zucchini, cucumber, spinach, shelled peas) and algae wafers to herbivores and omnivores. To blanch, simmer a slice for a minute or two, cool it, weight it so it sinks, and remove leftovers after a few hours.

Never feed

• Human food such as bread, crackers, cereal, meat, cheese, or anything salty, spiced or processed.
• Stale food. Vitamins break down once a container is opened; buy small containers and replace them within a few months.
• Feeder fish from unknown sources, a common way to bring in parasites and disease.
• Any food that has gone moldy or smells off.
• Extra helpings to be nice. Begging is a reflex, not a request.

Overfeeding — the signs

Cloudy water, a film on the surface, rotting food on the bottom, ammonia or nitrite above zero, sudden algae, and a foul-smelling gravel bed all point to too much food. Feed less, remove uneaten food after a few minutes, do a water change, and be patient. A fish that is a little hungry is a happy, healthy fish.

Shop the food and supplies: Browse Food for Aquatics.

Stocking & Compatibility

How many fish?

Forget "one inch of fish per gallon." For every species, ask: How big is it as an adult? How many does it need to be comfortable? How messy and active is it? Who will it get along with? The sum of the answers is your bioload, the total waste your fish produce and your filter and bacteria must handle. Keep it comfortably below what your biological filter can process.

As a starting point, a well-filtered 20 gallon long can hold one school of small fish (six to eight), a group of six small bottom dwellers, and a few livebearers or one centerpiece fish. A 29 gallon allows a second school or more variety. A single fancy goldfish is already a full 20 gallon tank's worth of waste. Planted tanks tolerate slightly more, but resist filling every inch in the first month.

Adding fish safely

1. Wait until the cycle is finished and ammonia and nitrite read 0 ppm.
2. Add a few fish at a time, not the whole list. A first group of four to six small fish is plenty; give the bacteria a few weeks to grow into the new load.
3. Test between additions. Ammonia or nitrite above 0 means pause, change water, and wait.
4. Add the hardiest species first and the more sensitive ones once the tank has matured.
5. Acclimate gently. Dim the lights. Float the sealed bag for about 15 minutes to match the temperature. Then add small amounts of tank water to the bag every few minutes over 20–30 minutes before netting the fish in. Do not pour the shop water into your tank.
6. Feed lightly for the first few days, and watch the fish for signs of stress.

Quarantine

Quarantine means keeping new fish in a separate tank for a few weeks before they join the others. It is the best insurance in the hobby, because many diseases show up days or weeks after purchase and one sick newcomer can infect an established tank. A plain 5–10 gallon tank with a sponge filter, heater, hiding places and no substrate is all you need. Keep new fish there for 2–4 weeks where possible, feeding well and watching for white spots, torn or clamped fins, odd swimming or poor appetite. Never share nets or siphons between tanks, and wash your hands between them. If you cannot quarantine, buy from a shop that does, watch the fish before you buy, and add newcomers slowly, a few at a time.

Compatibility

Research adult size and temperament before buying; a cute two-inch fish in a store may be a ten-inch predator in a year. As a rule, do not mix fin-nippers with long-finned fish, small fish with large mouths, or fast eaters with slow ones. Match water temperature and chemistry needs too.

Common Challenges & Solutions

Fish hide illness well, and by the time you see a symptom the underlying cause has usually been building for days. The fix for most problems begins in the same place: test your water first. Your test numbers and water-change log answer more questions than any medication does.

New tank syndrome and ammonia poisoning

What you see: fish gasping at the surface, clamped fins, red or inflamed gills, lethargy, hiding, or sudden deaths in the first weeks of a tank's life. Why: the nitrogen cycle is unfinished or has been disrupted (a filter rinsed in tap water, medication, too many fish too fast), so ammonia or nitrite are building up. What to do: test immediately, then do a 30–50% water change with dechlorinated, temperature-matched water, repeating daily until both read 0. Use a conditioner that also detoxifies ammonia temporarily, feed lightly, and add surface agitation. When to ask for help: if fish keep gasping or dying despite repeated water changes, or you cannot get readings to zero.

Ich (white spot disease)

What you see: tiny white spots like grains of salt on the body and fins, scratching against décor, clamped fins, and fast breathing. Why: a parasite (Ichthyophthirius), usually introduced on new fish and triggered by stress such as a temperature drop. What to do: the parasite is only vulnerable in its free-swimming stage, so treat for the full course on the label. Many keepers gradually raise the temperature toward the top of what their fish tolerate while using an ich medication labeled for freshwater. Scaleless fish such as corydoras and loaches are sensitive to some medications and to salt, so use reduced doses or ask the shop. Many treatments harm shrimp, snails and plants, so use a hospital tank when you can. When to ask for help: if spots persist after a full course, or fish struggle to breathe.

Fin rot

What you see: frayed, ragged or milky fin edges that slowly recede, sometimes with red streaks at the base. Why: bacteria attack fins weakened by poor water quality, stress or nipping. What to do: fix the water first, with small, frequent water changes and good filtration, and remove any nippers. If the rot progresses, use an antibacterial treatment as labeled, in a hospital tank. Fins regrow once the water is right. When to ask for help: if rot reaches the body or the fish stops eating.

Fungus

What you see: fluffy, cotton-like white or gray tufts on the body, fins or mouth, often at a wound. Why: fungus is usually secondary, invading tissue damaged by injury or poor water. What to do: correct water quality, remove the cause (rough décor, bullying), and use an antifungal as directed. When to ask for help: if growths spread or the fish cannot eat or breathe comfortably.

Velvet

What you see: a fine gold or rust-colored dust on the body, seen best when a flashlight shines across the fish at an angle, with clamped fins, rubbing and rapid breathing. Why: a fast-spreading parasite (Piscinoodinium) that can kill within days. What to do: act the same day. Dim the lights, do a water change, and treat with a velvet-labeled medication in a hospital tank if possible, since many contain copper that kills shrimp and snails. When to ask for help: immediately, especially if more than one fish is affected.

Swim bladder problems

What you see: a fish floating nose-up, sinking tail-first, swimming sideways, or struggling to stay level. Why: the swim bladder (the internal buoyancy organ) can be affected by constipation, overfeeding, gulping air with floating food, cold water or infection; round-bodied fancy goldfish are especially prone. What to do: check water and temperature, withhold food for a day or two, then offer a little blanched, shelled pea or soaked sinking food. Switch fancy goldfish to sinking food. When to ask for help: if it lasts beyond a week, comes with swelling or lesions, or the fish cannot eat.

Dropsy

What you see: a bloated belly and scales that stick out like a pinecone, sometimes with bulging eyes and pale, stringy droppings. Why: dropsy is a sign of internal fluid buildup from organ failure, often triggered by infection or long-term stress, not a disease by itself. What to do: move the fish to a quiet, clean hospital tank, keep the water pristine, and ask the shop or an aquatic vet about treatment. The honest news is that advanced dropsy is rarely curable; if a fish is suffering with no chance of recovery, humane euthanasia is the kindest choice, so ask an aquatic vet or the shop about the right method. Never flush a live fish. When to ask for help: at the first sign of swelling.

Internal parasites and wasting

What you see: white, stringy droppings, a sunken belly despite eating, weight loss and faded color. Why: intestinal worms and protozoa, often brought home on new or poorly fed fish. What to do: quarantine the fish and ask the shop about a suitable dewormer or medicated food; treat on a clear sign, since blind treatment is hard on fish. When to ask for help: if weight loss continues or more than one fish is affected.

Stress, aggression and fin nipping

What you see: hiding, faded color, a chased fish, torn fins, or a fish pinned in a corner or jumping. Why: wrong tankmates, too few in a school, too little space or cover, poor water, or a bully. What to do: review the compatibility table, add plants and hiding places, enlarge school sizes, and rearrange décor to break up territories; remove the aggressor if needed. When to ask for help: if injuries are open or the victim stops eating.

Cloudy water

What you see: water that looks milky, hazy or green. Why: it depends on the color. A milky white or gray haze in a new tank is a bacterial bloom, free-floating bacteria feeding on extra nutrients; it is common and usually clears within a week or two, so do not scrub everything or change all the water. Green water is free-floating algae from too much light and nutrients. Dust or debris usually comes from unrinsed substrate or stirred-up waste. What to do: test the water, feed less, cut the light to 6 hours, add filter floss, and keep up routine water changes. Clarifier products are no substitute for fixing the cause. When to ask for help: if cloudiness lasts beyond three weeks, smells foul, or comes with fish distress.

Algae

What you see: brown dust on glass and plants (diatoms, common in new tanks), green film or spots, hair-like strands, or dark tufts on leaves. Why: too much light, too many nutrients from overfeeding and waste, and too little plant growth. What to do: shorten the lighting period, move the tank out of sunlight, feed less, change water on schedule, and add fast-growing plants. Scrape glass and pull strands by hand; algae eaters help but cannot fix an imbalance. When to ask for help: if an outbreak keeps returning after all of this.

Quick reference

Routine Care Calendar

When to Ask for Help

Veterinary care for fish is rare, and aquatic vets are few. Your first call is usually your local fish shop, an aquarium club member, or us at (717) 983-8069. An aquatic or exotic vet can help when a fish is valuable, the problem is unclear, or an animal is suffering. When you are uncertain, ask. A five-minute conversation beats a week of guessing.

Act today:

• Any ammonia or nitrite reading in a tank with fish, particularly with gasping or clamped fins
• Fish gasping at the surface or crowding the filter outflow (bettas and gouramis taking an occasional breath are normal)
• Multiple fish sick or dying within a day or two
• A tank that suddenly turns milky and smells foul
• Heater failure, a stuck-on heater, or water far too hot or too cold
• Velvet, or white spots with fast breathing
• A fish with a bloated body and raised scales, or one that is stuck, trapped or badly torn
• Fumes or sprays near the tank (paint, smoke, aerosols, cleaning products), or a power outage lasting several hours
• Filter failure for more than a few hours in a stocked tank

Ask within a few days:

• A fish hiding, off its food, or faded for more than two days
• Frayed fins that are getting shorter
• White, stringy droppings or weight loss
• A fish floating or sinking oddly
• Persistent cloudy water or algae you cannot control
• Any lump, growth, or ulcer

Before calling, have your test numbers, tank size, species, stocking list, the date of your last water change, and photos or a short video of the fish ready.

FAQ

How long does it take to cycle a fish tank?

Most tanks take three to six weeks to cycle, though a seeded filter from an established tank and a bottled bacteria starter can shorten that, and cold water or low pH can stretch it to eight. The only reliable way to know is to test. Your tank is cycled when, 24 hours after adding about 2 ppm of ammonia, ammonia and nitrite both read 0 ppm and nitrate is present. Bottled bacteria help but do not remove the need to test.

What size tank is best for beginners?

A 20 gallon long or a 29 gallon is the best beginner minimum for a community tank. Bigger tanks are more forgiving because the same mistake gets diluted in more water and the temperature and chemistry change slowly, which gives you time to notice and fix problems. Small tanks of 5–10 gallons are best left to experienced keepers, a single betta (5 gallons minimum), or a shrimp colony.

How many fish can I put in my tank?

There is no reliable formula, and the old "one inch of fish per gallon" rule is a myth. Instead, consider each species' adult size, group needs, temperament and waste output, then add fish slowly and let your test results guide you. A well-filtered 20 gallon long usually holds one school of six to eight small fish, a group of small bottom dwellers, and a few extras; a fancy goldfish needs about 20 gallons by itself. When in doubt, understock.

How often should I change aquarium water?

As a starting point, change about 25–30% of the water weekly, using dechlorinated, temperature-matched water, and vacuum the gravel as you go. Adjust to your test results: if nitrate climbs above 20–40 ppm before the week is out, change more or more often; if your tank is lightly stocked and heavily planted, you may do fine with less. Consistency is more important than the exact number.

Why did my fish die after I set up a new tank?

The most likely cause is new tank syndrome: the nitrogen cycle was not finished, so ammonia and nitrite built up and poisoned the fish. Other common causes are untreated tap water, a sudden temperature change, adding too many fish at once, overfeeding, and stress from transport or incompatible tankmates. It is not your fault, and it is very common. Test your water, do water changes, and consider cycling fishless before trying again.

Do aquarium fish need a heater?

Tropical fish such as tetras, rasboras, corydoras, livebearers, bettas and most community species do, because they come from warm waters and do best at a steady 76–80°F (78–80°F for bettas), which most homes do not provide, particularly overnight. Goldfish are the exception: fancy goldfish prefer cool water (65–72°F) and generally do not need a heater in a normal home. In all cases, use a thermometer.

What are the best beginner fish?

Hardy, peaceful, small schooling fish are the classic starters: harlequin rasboras, black or ember tetras, corydoras, platies and zebra danios, kept in groups of six or more in a 20 or 29 gallon tank. A single betta in a heated, filtered 5 gallon tank is also a lovely first fish. Neon tetras are popular but can be delicate, so add them to a mature tank. Add fish slowly, a few at a time, once the tank is fully cycled.

How often should I feed aquarium fish?

Once or twice a day, in small amounts, only as much as the fish eat in about two minutes. Overfeeding is the second most common killer of aquarium fish; it fouls the water and fuels algae. Offer a quality staple flake or micro-pellet, add frozen foods such as bloodworms, brine shrimp or daphnia a few times a week, give blanched vegetables or algae wafers to herbivores, and consider one fasting day a week.

Can goldfish live in a bowl?

No. Goldfish produce a great deal of waste, grow larger than most people expect, and live 10–15 years or more, while a bowl has no filter, too little water, and too little oxygen. Fancy goldfish need a real aquarium of roughly 20 gallons for the first fish plus 10 for each additional, with strong filtration. Common and comet goldfish and koi grow too large for any home aquarium and belong in a pond.

Why is my aquarium water cloudy?

It depends on the color. A milky white or gray haze in a new tank is usually a bacterial bloom, which clears on its own in a week or two if you avoid overfeeding and over-cleaning. Green water is algae from too much light or too many nutrients. Dust or debris usually comes from unrinsed substrate or weak filtration. Test your water, feed less, cut lighting to 6 hours, and keep up regular water changes. If the water smells foul, look for a dead fish or rotting food.

Ready to shop? Start with Aquatics. 10% of every purchase supports no-kill animal shelters.

Every Purchase Gives Back

Before we earn a dime, 10% of every purchase at Walnut Creek Supply goes to no-kill animal shelters across the country. Not at checkout. Not as an option. Off the top of every order, every day, because we believe responsible pet ownership and community care are the same commitment made in two different directions.

For aquarium keepers, that commitment has one more dimension. Fish are not disposable, and they should never be released into a lake, stream or storm drain, where released fish and plants can devastate local waterways. If you ever need to rehome fish, contact your local fish shop, an aquarium club, or a rescue; most are glad to help. And if you love animals enough to read a guide this carefully, you are exactly the kind of keeper they deserve.

We are a family business in Christiana, Lancaster County, Pennsylvania. We grow our own food, keep our own animals, and stock the clean-label, USA-made goods we would put in front of our own families: no mystery ingredients, no junk fillers, and no care guide that skips the hard parts. If you have a question about your cycle, your test results, a new fish, or a problem you cannot solve, call us at (717) 983-8069. We would rather talk it through with you.

Welcome to a calmer corner of your home, and many years of watching your little underwater world thrive.

_From our family to yours,_ Walnut Creek Supply — Christiana, Lancaster County, Pennsylvania _walnutcreeksupply.com_

How long does it take to cycle a fish tank?

Most tanks take three to six weeks to cycle, though a seeded filter from an established tank and a bottled bacteria starter can shorten that, and cold water or low pH can stretch it to eight. The only reliable way to know is to test. Your tank is cycled when, 24 hours after adding about 2 ppm of ammonia, ammonia and nitrite both read 0 ppm and nitrate is present. Bottled bacteria help but do not remove the need to test.

What size tank is best for beginners?

A 20 gallon long or a 29 gallon is the best beginner minimum for a community tank. Bigger tanks are more forgiving because the same mistake gets diluted in more water and the temperature and chemistry change slowly, which gives you time to notice and fix problems. Small tanks of 5–10 gallons are best left to experienced keepers, a single betta (5 gallons minimum), or a shrimp colony.

How many fish can I put in my tank?

There is no reliable formula, and the old "one inch of fish per gallon" rule is a myth. Instead, consider each species' adult size, group needs, temperament and waste output, then add fish slowly and let your test results guide you. A well-filtered 20 gallon long usually holds one school of six to eight small fish, a group of small bottom dwellers, and a few extras; a fancy goldfish needs about 20 gallons by itself. When in doubt, understock.

How often should I change aquarium water?

As a starting point, change about 25–30% of the water weekly, using dechlorinated, temperature-matched water, and vacuum the gravel as you go. Adjust to your test results: if nitrate climbs above 20–40 ppm before the week is out, change more or more often; if your tank is lightly stocked and heavily planted, you may do fine with less. Consistency is more important than the exact number.

Why did my fish die after I set up a new tank?

The most likely cause is new tank syndrome: the nitrogen cycle was not finished, so ammonia and nitrite built up and poisoned the fish. Other common causes are untreated tap water, a sudden temperature change, adding too many fish at once, overfeeding, and stress from transport or incompatible tankmates. It is not your fault, and it is very common. Test your water, do water changes, and consider cycling fishless before trying again.

Do aquarium fish need a heater?

Tropical fish such as tetras, rasboras, corydoras, livebearers, bettas and most community species do, because they come from warm waters and do best at a steady 76–80°F (78–80°F for bettas), which most homes do not provide, particularly overnight. Goldfish are the exception: fancy goldfish prefer cool water (65–72°F) and generally do not need a heater in a normal home. In all cases, use a thermometer.

What are the best beginner fish?

Hardy, peaceful, small schooling fish are the classic starters: harlequin rasboras, black or ember tetras, corydoras, platies and zebra danios, kept in groups of six or more in a 20 or 29 gallon tank. A single betta in a heated, filtered 5 gallon tank is also a lovely first fish. Neon tetras are popular but can be delicate, so add them to a mature tank. Add fish slowly, a few at a time, once the tank is fully cycled.

How often should I feed aquarium fish?

Once or twice a day, in small amounts, only as much as the fish eat in about two minutes. Overfeeding is the second most common killer of aquarium fish; it fouls the water and fuels algae. Offer a quality staple flake or micro-pellet, add frozen foods such as bloodworms, brine shrimp or daphnia a few times a week, give blanched vegetables or algae wafers to herbivores, and consider one fasting day a week.

Can goldfish live in a bowl?

No. Goldfish produce a great deal of waste, grow larger than most people expect, and live 10–15 years or more, while a bowl has no filter, too little water, and too little oxygen. Fancy goldfish need a real aquarium of roughly 20 gallons for the first fish plus 10 for each additional, with strong filtration. Common and comet goldfish and koi grow too large for any home aquarium and belong in a pond.

Why is my aquarium water cloudy?

It depends on the color. A milky white or gray haze in a new tank is usually a bacterial bloom, which clears on its own in a week or two if you avoid overfeeding and over-cleaning. Green water is algae from too much light or too many nutrients. Dust or debris usually comes from unrinsed substrate or weak filtration. Test your water, feed less, cut lighting to 6 hours, and keep up regular water changes. If the water smells foul, look for a dead fish or rotting food.