Build a freshwater tank that actually stays stable.

Plan the tank first — get the real working volume in gallons, litres, and water weight before you buy anything, because every later dose, stocking choice, and equipment size depends on it. Cycle the tank for four to eight weeks before adding fish so beneficial bacteria can colonize the filter. Then choose compatible fish, size the heater and filter for the actual tank, and settle into a weekly water-change rhythm. The setup-path cards on the homepage walk through it in that order; the cycling guide and the aquarium volume calculator are usually the first two stops.

The aquarium volume calculator if you don't yet know the real working volume of your tank — every dosing, stocking, and equipment number depends on it. The compatibility checker before you buy fish at the store, so you don't bring home a stocking that fights or outgrows the tank. The ammonia or nitrite emergency calculator if a fish is already gasping, listless, or showing red gills. The water-change calculator for routine weekly maintenance once the tank is stable.

The compatibility checker compares parameter overlap (temperature, pH, hardness), tank-size minimums, schooling-group thresholds, predator-and-prey risk, aggression scores, and total bioload across your stocking plan. It gives you a conservative floor for whether a combination works — individual fish personality still matters, and a single rogue can void the model. Pair the checker with the species care guides for the husbandry context behind each verdict.

Treat it as urgent but not panic-worthy. Open the ammonia or nitrite emergency calculator, enter your current reading and tank volume, and follow the response math by severity tier — usually a partial water change combined with a dechlorinator dose that binds the toxic forms while the cycle catches up. Stop adding any new fish until ammonia and nitrite both read zero for at least a week. If the tank is new, the cycling guide and the new-tank-syndrome calculator cover what's normal week by week.

No. They are educational, beginner-safe decision support — math and sourced ranges that help you make better first decisions about volume, dosing, stocking, and equipment sizing. For sick fish, severe distress, or recurring deaths, consult an aquatic veterinarian or a qualified local aquarium professional. The calculator results give you specific numbers to bring into that conversation, which is usually more useful than a vague description.

FishBase for species anchors (taxonomy, native range, published temperature and pH and hardness tolerances). Manufacturer specifications for equipment sizing math. Aquaculture, veterinary, and fish-health references for disease and treatment guidance where available. Established hobby consensus from references like Aquarium Co-Op, Practical Fishkeeping, and Seriously Fish where primary sources don't answer aquarium-practice questions. Where sources diverge, the conservative beginner-safe answer wins.