Our Privacy/Cookie Policy contains detailed information about the types of cookies & related technology on our site, and some ways to opt out. By using the site, you agree to the uses of cookies and other technology as outlined in our Policy, and to our Terms of Use.


How Many Fish Should Be in a 55-Gallon Tank?

| Updated September 26, 2017

Rule of Thumb

A good guideline for determining the maximum number of fish to keep in any size tank is one inch of fish per one gallon of water.

Large Tanks are Different

In order to create a healthy environment for your fish, add only 10 inches of fish (so roughly two or three) and wait a month. Doing this creates the nitrogen cycle, a process that establishes helpful bacteria in the water and removes ammonia, which, in abundance, will kill your fish. Test the levels of ammonia and nitrite daily; once they return to zero, which means they are balancing themselves out, you can add more fish.

Bottom Line

The one-inch-per-gallon rule still applies, so be sure that you do not exceed 55 inches of fish in a 55-gallon tank. This roughly equates to four or five bottom-dwelling fish along with a couple algae eaters. For the happiest aquarium, buy community fish, those that coexist peacefully with other fish, such as rainbow fish, tetras or female bettas.