Molly: Tank Size, Tank Mates and Setup
A larger livebearer that needs more room than guppies or platies. Keep three or more in 20 gallons or larger.
- Minimum tank
- 20 gallons
- Temperature
- 75–80°F
- Group size
- 3 or more
- Adult size
- 4 inMiddle of the tank
- Does best in harder, alkaline water.
- Grazes on algae, so it produces a lot of waste for its size.
Poecilia sphenops. Figures are commonly published care ranges; see how it works.
How many mollies per tank size
The most you could keep if mollies were the only species. Open a size in the builder to add tank mates.
| Tank | Molly, kept alone | |
|---|---|---|
| 5 gallon | Too small (needs 20+ gal) | |
| 10 gallon | Too small (needs 20+ gal) | |
| 20 gallon | Up to 4 | Plan this tank |
| 29 gallon | Up to 7 | Plan this tank |
| 40 gallon | Up to 10 | Plan this tank |
| 55 gallon | Up to 14 | Plan this tank |
| 75 gallon | Up to 19 | Plan this tank |
What you need for mollies in a 20-gallon tank
A starting setup: 3 mollies in the smallest standard tank that suits them.
20-gallon tank
- These fit a 20-gallon tank and get along. Aim for about 78°F.
- Mollies breed readily. Keep males only if you don't want fry.
Equipment, sized for this tank
Starter supplies
Paid links. As an Amazon Associate, TankStarter earns from qualifying purchases. Sizes are estimates from published care guidelines, not hands-on testing.
Molly tank mates
These share a temperature range and temperament with mollies, with no warnings from our checks.
Use caution with: white cloud minnow, fancy goldfish, cherry shrimp, amano shrimp. Add them in the builder to see why.
Plan a tank around mollies
Add tank mates, check the stocking level and get the equipment sized for your tank.
Open the tank builderMolly questions
What size tank does a molly need?
At least 20 gallons for a group of 3. A larger tank is more stable and gives you more choice of tank mates.
How many mollies can I keep in a 20-gallon tank?
Up to about 4 if they are the only species in the tank. Fewer if you add other fish.
Do mollies need a heater?
Usually yes. Molly does best at 75–80°F, which is warmer than most rooms. A 20-gallon tank needs about 100 watts in a 68°F room.
What fish can live with mollies?
Good matches include bettas, neon tetras, cardinal tetras, ember tetras, rummy-nose tetras, black skirt tetras. They share a temperature range and temperament with mollies.