About 5–6 — based on adult size, bioload, and real water volume.
In a 40-gallon tank you can comfortably keep about 5–6 kuhli loach — 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 kuhli loach reaches about 4.0" and has a moderate bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 40-gallon tank supports roughly 5–6 of them. Because kuhli loach are schooling fish, keep them in a group of at least 5 — never just one or two. They need 73–86°F water at pH 6–7.
Build your exact stocking with the calculator → Full kuhli loach care guide →
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