Calculate safe fish stocking levels
Maximum Fish Inches
29
total inches of fish
Small Fish
19
(1-2")
Medium Fish
8
(3-4")
Large Fish
5
(5-6")
Moderate - Weekly maintenance
Stock Gradually
Add fish slowly over weeks to let your filter bacteria adjust.
Consider Adult Size
Always calculate based on adult fish size, not current size.
Inputs
Result
Max inches = 29 x 1.0 = 29. Small fish = floor(29 / 1.5) = 19. Medium = floor(29 / 3.5) = 8. Large = floor(29 / 5.5) = 5. Filter = 29 x 5 = 145 GPH. Bioload: Moderate.
Inputs
Result
Max inches = 55 x 0.5 = 27.5, rounded to 28. Small fish = floor(27.5 / 1.5) = 18. Medium = floor(27.5 / 3.5) = 7. Large = floor(27.5 / 5.5) = 5. Filter = 55 x 8 = 440 GPH. Bioload: High.
The classic rule is 1 inch of fish per gallon of water. However, this is a simplification - adult fish size, body shape, and bioload all affect true stocking capacity.
Goldfish produce much more waste than tropical fish of similar size. They need 10+ gallons per fish minimum, while many tropical fish can thrive in smaller spaces.
Your filter should turn over the tank volume 4-5 times per hour for tropical fish, 8-10 times per hour for goldfish or messy fish like cichlids.
Cycle your tank for 4-6 weeks before adding fish so beneficial bacteria can establish. Then add only a few fish at a time over several weeks.
Calculate needs for all your animals
Last Updated: Feb 12, 2026
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