How Many Glowlight Tetras in a 40 Gallon Tank?
About 22–27 — based on adult size, bioload, and real water volume.
In a 40-gallon tank you can comfortably keep about 22–27 glowlight 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 glowlight 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 glowlight tetra are schooling fish, keep them in a group of at least 6 — never just one or two. They need 74–82°F water at pH 5.8–7.5.
Build your exact stocking with the calculator → Full glowlight tetra care guide →
Gear for a 40-gallon tank
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