Aquarium Stocking Calculator

No — it's a widely used starting-point heuristic, not a precise bioload calculation. It doesn't account for real differences between species in body mass, activity level, waste production, or adult size (a fish that looks small as a juvenile in the store can grow well past its stocking assumption), so it should be treated as a rough first estimate to refine with species-specific research, not a hard limit.

Saltwater fish and reef corals generally produce more waste and need more dissolved oxygen and more stable water chemistry per inch of livestock than typical freshwater community fish, and reef tanks specifically also need to support the coral's own biological demands on top of any fish. That's why this calculator applies a stocking rule roughly five times more conservative for saltwater and reef tanks than for freshwater.

This calculator can adjust your base stocking allowance from 60% up to 120% depending on turnover rate — a filter processing under 3x the tank volume per hour cuts the recommendation to 60% of the base rule, while a filter hitting 6x or more turnover raises it to 120%, since stronger, more consistent filtration removes waste and maintains water quality more reliably at higher stocking density.

The recommendation is deliberately set at 75% of the filtration-adjusted maximum as a safety margin, because both the base inches-per-gallon rule and the filtration adjustment are still simplified guidelines rather than a precise bioload model for your specific fish species — leaving headroom reduces the risk of overstocking from the inherent imprecision of a rule-of-thumb approach.