What Size Tank Does a Molly Need?
Minimum tank: 20 gallons
A Molly (Poecilia sphenops) grows to about 4 in (10.2 cm), so the practical minimum is a 20-gallon aquarium. A pair or small group is typical, so leave a little extra room for tankmates.
| Single fish or pair | 20 gallons |
|---|---|
| Comfortable group | 20 gallons |
| Community setup | 30 gallons+ |
Bigger is easier: more water dilutes waste and holds temperature and pH steady. See stocking ideas for a 20-gallon tank or try the stocking calculator.
Frequently asked questions
What is the minimum tank size for a Molly?
At least 20 gallons.
Can a Molly live in a smaller tank?
Going under 20 gallons stresses the fish, worsens water quality and shortens its life — not recommended.
More on this species: Molly full care guide · tank size · temperature · pH & hardness · tank mates