Quick answer
Is my 10-gallon tank overstocked?
A 10-gallon (about 38-liter) tank is overstocked when its bioload outruns its filtration and surface area — not at a fixed fish count. Common signs are nitrate rising fast between water changes, fish gasping at the surface, and needing more than a ~25% weekly change to hold parameters steady.
Forget 'one inch of fish per gallon' — it ignores body mass, waste output and tank shape. A 10-gallon suits a small group of nano fish (a single betta, a shoal of 6–8 small tetras or rasboras, or a shrimp colony), but the same gallons are badly overstocked with a goldfish, or a handful of full-grown fancy guppies plus a pleco.
The honest test is your own water: if nitrate climbs quickly, the tank struggles to hold oxygen, or aggression spikes in the tight space, you're over capacity. Reduce stock, upgrade filtration, do larger water changes — or move up to a bigger tank. The stocking calculator turns your exact list into a percentage so you can see where you stand.
Check it against your tank
Every tank is different. Enter your real dimensions and stock list to get a bioload-based stocking level, a filtration check and compatibility warnings for your exact setup.
Open the Stocking CalculatorRelated
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