Aquarium Stocking Calculator
Aquarium Stocking Calculator
How many fish can your tank hold?
How to Use This Calculator
Enter Tank Size
Type your aquarium's volume in gallons. This is the single biggest factor in how many fish you can safely keep.
Select Fish Species
Choose your primary fish species. Each fish has different space, bioload, and water quality requirements.
Set Filtration & Plants
Better filtration and live plants significantly increase how many fish your tank can support by processing more waste.
How We Calculate Stocking Levels
This calculator uses a modified "gallons per fish" method that accounts for species-specific space requirements, bioload (waste production), filtration capacity, and plant density. The standard "1 inch per gallon" rule is outdated and dangerous for large or high-bioload fish.
Bioload factors are based on adult fish size and metabolic waste production rates. Goldfish and Oscar Fish produce 3–4× more ammonia per body weight than small schooling fish like tetras and rasboras.
Filter ratings follow the turnover rate method: excellent filtration processes tank volume 3–5× per hour, good at 2–3×, and average at 1–2×. Live plants, especially fast-growing species, can absorb significant nitrates and effectively increase safe stocking density by 10–25%.
Sources & References
- Fishbase.org Species Database
- American Cichlid Association Care Sheets
- Aquatic Community Forum Bioload Research (2024)
Data last verified:
Aquarium Stocking — Common Questions
ToolSite Team
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