How Many Fish Can I Put in My Tank?

The old “one inch per gallon” rule is a rough starting point, not a law. A ten-inch pleco does not belong in a ten-gallon tank. Look up adult size, swimming style, and social needs before you buy.

For a typical 20-gallon community tank, a modest group of small tetras or rasboras plus a few bottom dwellers is reasonable. Add two or three fish per week at most so filter bacteria can expand. Jumping to a full stocking list on day one is a common cause of ammonia spikes.

If nitrate climbs fast despite weekly changes, fish hide constantly, or you see gasping at the surface, you may be overstocked. ReefDiary helps track livestock count and parameter trends so stocking decisions are based on data, not the bag size at the store.