About FishFits

What you can do here

Many common fish problems start before the fish come home: a tank that's too small, tank mates that fight, or water that suits one fish but not another. Our tools help you spot these problems while you're still planning.

How we work

• Researched data with a clear method. Each species is researched from at least two reputable sources and then fact-checked. Values describe healthy long-term keeping, not the limits a fish can survive. When sources disagree, we use the conservative value. Each species page lists its sources and when it was last reviewed. Read our editorial policy and the full list of sources.
• Every warning is explained. Our stocking calculator weights fish by adult size and waste instead of the "one inch per gallon" rule. When it flags a problem, it tells you which fish caused it and why. The exact rules are on our methodology page, and the formulas are shown on each calculator.
• Private by design. No accounts and no sign-up. Plans you save to My tanks stay in your browser and are never uploaded. See our privacy policy.
• No paid placements. No shop or brand pays to be included or to change a result. Some shop links may earn us a commission, and we explain this in our affiliate disclosure.

What our tools can't do

Our results are estimates based on typical, healthy fish. Individual fish vary, and your water, filter and maintenance matter a lot. Use the tools to plan, then watch your fish and test your water. For sick fish, ask an aquatic vet or an experienced local fish store. Read our terms of use.

Get in touch

Spotted an error, want a species added or have an idea for a tool? Email [email protected] or see our contact page. Changes to our data and calculators are listed in the changelog.