About 57–69 — based on adult size, bioload, and real water volume.

In a 55-gallon tank you can comfortably keep about 57–69 ember 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.
An adult ember tetra reaches about 0.8" and has a low bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 55-gallon tank supports roughly 57–69 of them. Because ember tetra are schooling fish, keep them in a group of at least 8 — never just one or two. They need 73–84°F water at pH 5.5–7.
Build your exact stocking with the calculator → Full ember tetra care guide →
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