Why this site exists
Search for aquarium stocking advice and you get two kinds of result: shops that would like to sell you the fish, and calculators built on a single rule of thumb from the 1960s that was never right in the first place. One inch per gallon treats a six-inch goldfish as equivalent to six neon tetras, ignores whether the fish will eat each other, and cannot see a filter, a footprint or a water surface.
We do not sell livestock, plants or equipment, and we take no commission from anyone who does. The species database is the whole product here — adult sizes, minimum tank lengths, schooling minimums, temperature, pH and hardness ranges, temperament and bioload for the freshwater species people actually keep.
Where we will disagree with someone
Fish compatibility is genuinely contested. Two experienced keepers will tell you opposite things about serpae tetras, about whether a betta belongs in a community tank, and about how many gallons an oscar needs — and both will have kept the fish for years.
So the rules here are deliberately conservative. Where the hobby disagrees, the species note says so instead of picking a side. Where we are not sure, the matrix shows a caution rather than a tick. And where we are not confident about a species at all, it is left out of the database rather than guessed at — a wrong entry is worse than a missing one.
If you think a figure is wrong, tell us. That is the whole correction policy.