Free Freshwater Tool
Plan your perfect fish community. Check stocking levels, species compatibility, and school size requirements — all in seconds.
Effective Capacity
—
No fish added yet.
Browse species and tap + to add.
Enter your aquarium size in gallons. We account for gravel, decor, and filter quality to calculate your effective water volume.
Browse 25+ popular freshwater species. We automatically enforce minimum school sizes for social fish.
Instant alerts for overstocking, incompatible species, undersized tanks, and incomplete schools.
The classic rule suggests one inch of adult fish per gallon of water. Our calculator improves on this by using bioload multipliers — slim fish like tetras produce less waste than heavy-bodied fish like goldfish, so they "cost" less capacity.
We subtract 10% of your tank volume for gravel, decorations, and equipment displacement. If you have a good or excellent filter, we add 10-20% back as extra biological capacity.
Many freshwater fish are schooling species that become stressed and aggressive when kept alone or in small groups. Our tool enforces minimum group sizes and warns you when a school is incomplete.
This calculator provides general guidance only. Many factors affect stocking: plant density, water change schedule, feeding habits, and more. Always research each species thoroughly and cycle your tank before adding fish. When in doubt, stock less.