Aquarium Stocking Calculator

Aquarium Stocking Guide

The Inch Per Gallon Rule

The traditional rule is 1 inch of fish per gallon (roughly 2.5cm per 4 litres). Modern practice refines this: use body length excluding tail, apply lower densities for deeper-bodied fish, and reduce stocking if filtration is average.

Overstocking Consequences

Too many fish leads to ammonia spikes, oxygen depletion, and disease. The nitrogen cycle can only process a certain biological load — overstocking overwhelms beneficial bacteria even in a mature tank.

Build Slowly

Never add all fish at once. Add no more than 20–25% of your final stocking at one time. Test water chemistry for 2 weeks between additions. A well-cycled, lightly stocked tank is the foundation of a healthy aquarium.