In the order you need them
Straight answers on tanks, cycling, and what fish you can actually keep — written for people setting up their very first aquarium.
These guides follow the order you actually need them in: choosing a tank and working out what it really costs, the equipment that matters (filter, heater, light, substrate) and what you can skip, the nitrogen cycle and how to run a fishless cycle properly, then stocking — beginner-friendly fish, easy live plants — and the maintenance routine that keeps it all stable.
Every guide is written by a named human author who keeps tanks, gives you the numbers to test against rather than vague advice, and gets updated when better information turns up. Read more about our editorial standards.
What a 20 gallon fish tank setup costs in 2026, item by item: about $230 on a tight budget, $400–$500 done properly with a stand, and $10 a month to run.
A 20 gallon fish tank costs about $230 to set up on a tight budget and $400 to $500 done properly with a stand, before fish. Fish add $30 to $80, and running it costs roughly $10 a month. The tank itself is the smallest part of the bill.
Can you use distilled water in a fish tank? Not by itself — it has no minerals and cannot hold a stable pH. Use it for top-offs and to soften hard tap water.
Do not fill a fish tank with distilled water alone. It has no minerals for the fish and no carbonate to hold the pH steady. Use it to top off evaporation and to dilute hard tap water, and use dechlorinated tap water for everything else.
How to change fish tank water: replace 25% once a week, with new water dechlorinated and matched to within 2°F. The steps, and how to set your own schedule.
Change 25% of the water once a week. Siphon the old water out through the gravel, refill with tap water that is dechlorinated and within 2°F of the tank, and leave the fish where they are. Test nitrate before each change to check the schedule is enough.
Scuds in an aquarium are tiny curled crustaceans that swim on their side. With fish they are free live food. With only shrimp they are a rival.
Scuds are small freshwater amphipods that arrive on live plants. In a tank with fish they are harmless and most fish eat them. In a shrimp-only tank they outbreed and outcompete the shrimp, and no treatment removes them without risk to the shrimp as well.
Snail eggs in a fish tank look different for every species. Identify yours in one table — clear jelly, pink clutch or hard white dots — and if they will hatch.
Clear jelly blobs on the glass or plants are pest snail eggs and will hatch in one to three weeks. A pink honeycomb above the waterline is a mystery snail clutch. Hard white dots like sesame seeds are nerite eggs, and those never hatch in freshwater.
Why does my fish tank smell? A healthy tank smells like damp soil. Rotten eggs, rotting fish and musty swamp each point to one cause — matched in one table.
A healthy fish tank smells faintly of damp soil. A rotting smell means something dead or uneaten food, rotten eggs means an oxygen-starved pocket in the sand or a filter that stopped, and a heavy musty smell is usually cyanobacteria. Find the source before you change any water.
Detritus worms in a fish tank are harmless waste eaters. A sudden bloom means overfeeding — and here is how to tell them apart from planaria, which are not.
Harmless. Thin white worms wriggling in the substrate of a fish tank are detritus worms, not parasites — they eat waste. A sudden bloom means overfeeding, so cut food and vacuum the substrate. Do not medicate.
How many fish in a 10 gallon tank? Six to eight small schooling fish, or one betta plus a clean-up crew — and why inch-per-gallon keeps killing tanks.
Six to eight small schooling fish, or one betta plus a clean-up crew. The inch-per-gallon rule is wrong — it ignores adult size, waste output and swimming space, and it is why beginner 10-gallon tanks crash.
How much does a fish tank weigh? A filled 55 gallon comes to around 625 lb. Full weight table by tank size, plus what your floor can actually take.
A filled 55 gallon fish tank weighs roughly 625 lb — about 460 lb of water, 78 lb of glass and 55 lb of substrate. That is concentrated on roughly four square feet, which is why the floor matters as much as the stand.
How to acclimate fish to a new tank: float the bag 15 minutes, add tank water every 5 minutes for 20, then net them in. Never pour the bag water in.
Acclimate a new fish by floating the sealed bag for 15 minutes to match temperature, then adding a quarter-cup of tank water every 5 minutes for 20 minutes. Net it in — never pour the bag water into the tank.
How to clean aquarium decorations: hot water and a toothbrush for most of it, a 1:9 bleach soak for stubborn algae, then rinse and dechlorinate. Never soap.
Clean aquarium decorations by scrubbing them in hot water with a toothbrush kept only for the tank. Never soap. For algae that will not come off, soak 10 minutes in 1 part bleach to 9 parts water, rinse, then dechlorinate before it goes back.
Pothos in an aquarium is safe for fish and a strong nitrate exporter — roots in the water, leaves in the air. The real risk is the pesticide on the plant.
Yes — pothos in an aquarium is safe, and one of the best nitrate exporters for a beginner tank. Roots in the water, leaves in the air. Submerging the leaves kills the plant, and an unquarantined shop plant can kill shrimp.
What temperature should a fish tank be? 76-78°F suits almost every community tank. Bettas want warmer and goldfish cooler — which is why they cannot share.
A fish tank temperature of 76-78°F (24-26°C) suits almost every beginner community tank. Bettas want 78-80°F and goldfish want 65-72°F, and the two cannot share a heater setting — which is the real reason they cannot share a tank.
Ammonia, nitrite and nitrate in plain English — how to run a fishless cycle step by step, and the one test that tells you the tank is ready for fish.
Run a fishless cycle with bottled ammonia for three to six weeks. The tank is ready when a dose of 2 ppm ammonia reads 0 ammonia and 0 nitrite within 24 hours — not before.
Small tanks are sold as beginner tanks but are the hardest to keep stable. How 5, 10, 20 and 29-gallon tanks compare on stocking, cost and forgiveness.
Buy a 20-gallon long. It is dramatically more forgiving than a 5 or 10, costs perhaps $30 more than the 10, and is the single biggest thing you can do to keep your first fish alive.
