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How many neon tetras in a 20-gallon tank?

A 20-gallon (about 75-liter) tank comfortably holds 10–15 neon tetras on its own, leaving room for filtration and a small clean-up crew. If the neons share the tank with other fish, plan on fewer.

Neon tetras are small, light-bodied schooling fish with a low bioload, so a 20-gallon tank has plenty of capacity for one large shoal. Keeping them in a group of at least 6 — ideally 10 or more — matters most: bigger schools are calmer, bolder and healthier. A group of 12 looks fantastic and stays well within the tank's bioload.

The real limit isn't the tetras alone but everything together. Add corydoras, a centerpiece fish or shrimp and the combined bioload climbs, so reduce the tetra count to match. Long, shallow 20-gallon tanks (the '20 long') support a touch more than tall ones because surface area drives gas exchange.

Searching for a 20-litre tank instead? That's a very different size. A 20-gallon tank holds about 75.7 liters (20 × 3.785), while 20 liters is only about 5.3 US gallons, a quarter of the volume. A 20-liter nano is too small for neon tetras, which need room to swim as a group in at least 40 liters. In 20 liters, keep shrimp, snails or a single betta instead, and save neons for a tank of 10 gallons (38 L) or more.

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Frequently asked questions

How many tetras can I keep in a 20 gallon tank?
About 10–15 small tetras such as neon, ember or black neon tetras if they are the only school, or 8–10 if the tank also has other fish. Larger tetras such as black skirt, serpae or congo tetras produce more waste, so keep a smaller group of 6–8.
What is the minimum tank size for neon tetras?
About 40 liters (10 US gallons), with at least 45 cm (18 in) of swimming length, for a small school of 6–8. Neon tetras are active schooling fish, so a longer tank of 20 gallons (75 liters) or more lets you keep a proper group.
How many fish can I put in a 20 gallon long?
A 20 long (30 × 12 × 12 in, about 71 liters) suits a community of roughly 15–20 small fish, for example 10–12 tetras or rasboras, six pygmy corydoras and a few snails. Its long footprint holds slightly more than a 20 high of the same volume.
Can neon tetras live with a betta?
Often, yes: in a planted tank of 20 gallons (75 liters) or more, kept at 24–26 °C where both are comfortable. Watch the first week closely, because a few bettas will chase small fish.

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