FishTankSizes.comThe aquarist’s blueprint and field guide

Fishkeeping guides

In-depth guides to choosing, setting up and running a freshwater tank. Every factual claim links to its source.

Best first tank sizeBigger than you think. Most sources point beginners to 20 to 40 gallons, because more water is more forgiving.Cycling a new tankA new tank has no bacteria to process fish waste. Cycling grows them first, and it usually takes four to eight weeks.Water changesAbout a quarter of the water each week suits most tanks. Your nitrate reading tells you whether yours needs more.Filter flow rate (GPH)Aim for a filter rated at four to six times your tank’s volume per hour, then expect it to move less than the box says once it is full of media.Aquarium heater sizeMost sources land between 3 and 5 watts per gallon. The right end of that range depends on how cold your room gets, not just on the tank.Choosing substrateGravel is the easy default. Sand suits bottom-sifting fish, soil suits plants, and crushed coral or aragonite is for hard-water fish.Stands and floor weightA filled tank weighs about 10 pounds per gallon and puts all of it on a small patch of floor. Here is how to place one safely.Glass vs acrylicGlass is cheaper and resists scratches. Acrylic is lighter, tougher and clearer at thickness, but scratches easily and needs full support underneath.Quarantine tank setupA cheap second tank where new fish spend about a month before they meet the rest. It is the best protection against bringing disease home.Moving a fish tankEmpty it completely, keep the filter media wet, and treat the restart like a lightly stocked new tank for a couple of weeks.

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