Plan a freshwater tank before you buy the fish

The score is not one judgement but four, and each is shown on its own so you can see where the marks went. Company asks whether these species can live together, or whether one is known to nip, harass or eat another. Room asks whether there is space for them at the size they grow to, not the size they are sold at.

Water asks whether there is a temperature, a pH and a hardness every one of them is comfortable in at once, and how narrow that shared window is. Shoal size asks whether each shoaling fish has enough of its own kind to feel safe. Every deduction comes with a sentence saying what it is and what would get the marks back.

The old rule counted inches of fish against gallons of water, which lets one large fish into a tank it can barely turn around in and treats a shoal of tiny fish as if they were one medium one. Here, room grows faster than length does for bigger fish, and the smallest fish get a floor so a crowd of them still reads as a crowd. Shrimp and snails claim a fraction of what a fish their length would.

Planting, filtration and water changes earn the tank a little extra headroom, and the credit is capped, so good husbandry can make a full tank comfortable, and bring one just over the line back under it, but it cannot rescue a badly overstocked tank. The level comes back in words as well as a figure, from room to spare through comfortably stocked and nearly full to overstocked.

Comfortably stocked means there is still a margin for the things that go wrong in real tanks, such as a fish that grows past what you were told, a filter that lapses, or a hot week. Nearly full means nothing is wrong and nothing more should go in. Overstocked is never a refusal, because the remedy is always in your hands. Keep fewer fish, or score a bigger tank instead.

A finding that blocks is different. It means a species has a hard requirement this tank does not meet, such as a minimum volume or a minimum length for a fish that swims the glass. Those are not worked out here; they come from the fish's own page, and the footnote there says where from. A gap in what is known is reported as a gap, never filled in with a plausible number.

The suggestions beside your tank are the species Finform would add next. Each one is scored as if it were already in the tank, and any that would be a risk to something you already keep is held back rather than offered with a warning attached. Fish come before shrimp and snails, and a species whose group size is not on record is shown with a dotted edge, so a guess is never dressed as a fact.

The preset tanks above are found the same way. Each is a stocking that passes clean as it stands, unplanted, so planting is an upside rather than a crutch, and each is scored again every time the page is drawn, from the exact link on its card. The number on the chip is the number you land on.