Freshwater Aquarium Stocking Calculator

How this calculator works

Each selected species contributes adult-size load units. The load is adult size in centimeters times a multiplier from the species bioload label: very low, low, medium, or high. Tank capacity is based on volume and adjusted for light, standard, or strong filtration.

This is a heuristic for comparing reasonable freshwater plans. It deliberately avoids inch-per-gallon rules because those ignore body shape, waste production, adult size, schooling needs, and behavior.

Why it matters

Thin stocking advice often says only whether a fish fits a tank. Useful planning asks whether the adult group fits, whether the filter has margin, and whether the minimum-tank figure is being ignored. This calculator makes those tradeoffs visible before livestock is purchased.

Worked example

Six neon tetras in a 15 US gallon tank create a modest load because they are small and marked low bioload. Adding a high-bioload bottom dweller can push the same tank close to capacity even if the inch count still appears low.

FAQ

Is this inch-per-gallon stocking?

No. It uses adult size, the site bioload label, tank volume, and filtration level as a planning heuristic.

Does it check compatibility?

No. It estimates load and flags group-size or minimum-tank issues; use compatibility pages for tank-mate risk.

Can filtration make any stock list safe?

No. Strong filtration helps waste processing, but it does not fix aggression, adult size, oxygen demand, or swimming space.

Why use adult size?

Juveniles grow. Planning from adult size reduces the chance of building a tank that only works temporarily.