How Many Neon Tetras in a 40 Gallon Tank?
About 22–27 — based on adult size, bioload, and real water volume.
About 22–27 neon tetra
Photo via Wikimedia Commons
In a 40-gallon tank you can comfortably keep about 22–27 neon tetra — enough for a proper school, on their own with good filtration and regular water changes. Add fewer if you're mixing in other species.
How we get that number
An adult neon tetra reaches about 1.5" and has a low bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 40-gallon tank supports roughly 22–27 of them. Because neon tetra are schooling fish, keep them in a group of at least 6 — never just one or two. They need 70–81°F water at pH 6–7.
Build your exact stocking with the calculator → Full neon tetra care guide →
Gear for a 40-gallon tank
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FAQ
How many neon tetra can I keep in a 40 gallon tank?
About 22–27 neon tetra, kept on their own with good filtration. Add fewer when combining with other species — use the stocking calculator to be sure.