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Aquarium stocking calculator
Choose your tank and the animals you want. We check tank size, group size, tank mates and shared water, using the same figures as our species pages.
Your tank
Add an animal to start.
Each one starts at the minimum group size in our data.
How this works
- Tank size uses the sourced minimum for each animal, with a 10% allowance.
- Group size uses the sourced minimum group for each animal.
- Tank mates uses the same rating as our species pages for every pair you choose.
- Water shows the temperature, pH and hardness ranges all your animals share. If a figure is not published, we say so and leave that animal out of the range.
It does not estimate how many fish your tank can hold. Our first-tank guide explains why the old rules of thumb disagree. Before anything goes in, cycle the tank, and bring animals home a few at a time.
Frequently asked questions
Why is there no percent-stocked number?
Because we found no sourced method that can honestly give one. The usual rules of thumb disagree with each other, as our first-tank guide shows, and the true limit depends on filtration, territory and how the animals behave. A precise-looking percentage would suggest a certainty we do not have.
How do you decide which animals can live together?
Each pair is rated from the water figures on our species pages and from behavior notes in our sources, with a few pairs set by hand from sources we read. Both directions are checked, and the stricter one wins. Species pages show the same ratings.
If nothing is flagged, is my plan safe?
Not necessarily. These checks do not measure how much waste your animals make, how well your filter copes, or how individual fish behave. Cycle the tank first, add animals slowly, and test the water.
Why does a species use a tank size I think is too big or too small?
Minimums come from the sources named on each species page, and hobby sources often disagree. Follow the link to see the source. If you have a better one, you can report a correction.
This tool is educational and is not veterinary advice. Read our disclaimer. Spotted something wrong? Report a correction.