How Many Swordtails in a 20 Gallon Tank?
Too small for a healthy school — based on adult size, bioload, and real water volume.
A 20-gallon tank is really too small for a proper group of swordtail — they're a schooling fish that needs at least 3 to feel secure. Step up to a bigger tank, or pick a smaller schooler.
How we get that number
An adult swordtail reaches about 5.5" and has a heavy bioload. Working from real water volume and waste output (not the old one-inch-per-gallon myth), a 20-gallon tank supports roughly too small for a healthy school of them. Because swordtail are schooling fish, keep them in a group of at least 3 — never just one or two. They need 70–82°F water at pH 7–8.4.
Build your exact stocking with the calculator → Full swordtail care guide →
Gear for a 20-gallon tank
As an Amazon Associate we earn from qualifying purchases.