Can Bettas Live With Mollies?
Edited by Ivan F.
Short answer
With caution
With caution. Mollies are peaceful and rarely start trouble, but they want much harder water than most bettas are kept in, and they need a bigger tank.
The main problem here is the water rather than aggression. Mollies suit hard, alkaline water, and their published hardness range meets a betta's only at the very top of the betta's range. They also grow a little larger than a betta, live in groups and breed freely, which together add a lot of waste and traffic to the tank.
How they compare
Figures come from our species pages. Shared ranges are where both animals are comfortable.
Betta and Molly
- Adult size
- Betta: 2.8 in (7 cm)
- Molly: 3.1 in (8 cm)
- Minimum tank
- Betta: 11 US gal (41 L)
- Molly: 21 US gal (81 L)
- Temperature
- Betta: 72–86°F (22–30°C)
- Molly: 70–82°F (21–28°C)
- pH
- Betta: 6–8
- Molly: 7–8.5
- Hardness
- Betta: 1–15 dGH
- Molly: 15–30 dGH
- Temperament
- Betta: Territorial/Aggressive
- Molly: Peaceful
- Swim zone
- Betta: Top
- Molly: Top
Shared by both
Temperature: 72–82°F (22–28°C)
pH: 7–8
Hardness: 15 dGH
Largest species minimum
21 US gallons (81 L), from Molly. This is a starting point, not a stocking plan.
What to watch for
- Test your water first, because soft water that suits many bettas does not suit mollies.
- Choose short-finned mollies, since long fins can trigger a betta. Guides disagree on sailfin and lyretail types.
- Females can give birth repeatedly, even without a male present, so have a plan for the fry.
- Male mollies squabble among themselves, and that commotion can stress a betta.
Tank setup
Gear for the largest setup on this page
A forgiving setup with room for a small community.
Tank size for the largest species (Molly)
At least 21 US gallons (81 L)
Filter
Hang-on-back or large sponge filter
Easy to maintain and strong enough for a community without blasting the fish.
We are still choosing products for this.
Heater
Adjustable heater, about 5 W per gallon: 100 W at 20 gallons, about 150 W at 29
Enough power to hold a stable temperature in most homes. Size up for a cold room.
We are still choosing products for this.
Water Conditioner
Dechlorinator such as Seachem Prime
Tap water contains chlorine or chloramine that harms fish.
Seachem Prime US
Fritz Complete Water Conditioner US
API Betta Water Conditioner US
sera aquatan Spain
Tetra AquaSafe Spain
Maker's page · Sold at Kiwoko · Sold at Tiendanimal · Sold at zooplus.es
Why we chose these (Best Water Conditioner for Betta Fish). Nobody here has used or tested them.
Test Kit
Liquid kit such as API Freshwater Master
Tracks ammonia, nitrite, nitrate and pH while the tank cycles.
API Freshwater Master Test Kit US
API General & Carbonate Hardness Test Kit US
Maker's page · Sold at The Shrimp Farm · Sold at Bulk Reef Supply
sera aqua-test box (Cl) Spain
JBL PROAQUATEST COMBISET Plus NH4 Spain
Why we chose these (Best Test Kit for a Freshwater Aquarium). Nobody here has used or tested them.
Cycle the tank before adding animals. See our guide on how to cycle a fish tank.
Frequently asked questions
Do mollies need salt to live with a betta?
One guide says mollies raised in fresh water do fine without it, and that some betta keepers use aquarium salt anyway. Ask how your mollies were raised before you buy.
Will a molly attack a betta?
That is unusual, as mollies are generally peaceful, though there is a small chance of fin nipping. The betta is the more likely aggressor, so watch the mollies for damage in the first few days.