Yes: Compatible.
No clashes under our rules: they share a temperature range, neither is a fin nipper or predator of the other, and their temperaments fit.
Temperature. Betta (male) does best at 24–30 °C (75–86 °F) and Molly at 21–28 °C (70–82 °F). They share 24–28 °C.
Water. Their pH ranges overlap at 7–8.
Temperament and size. Betta (male) is semi-aggressive and grows to 7 cm; Molly is peaceful and grows to 8 cm. Betta (male) swims at the top and Molly at the mid, which spreads them out.
Tank size and groups. Plan on at least 30 US gallons, the larger of the two cautious minimums. Keep Molly in a group of 3+. A starter mix of 1 Betta (male) and 3 Molly in 30 gallons uses about 36% of the tank’s bioload capacity under our rules and grades A.
Keeping them together
- Feeding: both feed in open water. Feed small amounts two or three times a day so the slower eater gets its share.
- Aquascape: break up sight lines with plants, wood or rock, and give each fish its own hiding spots. Territorial fish settle faster when they can’t see each other all the time.
- Group size: a full group is not optional. A schooling fish kept in too small a group is stressed and more likely to nip or hide.
- Shrimp and snails: neither is a known invertebrate eater, but baby shrimp can still be eaten. Dense moss helps.
- Adding them: add the calmer species first and let it settle for a week or two before adding the other, and only once your tank has cycled.
Open this pair in the checker Add your other fish to grade the whole tank.
Quick facts
| Betta (male) | Molly | |
|---|---|---|
| Adult size | 7 cm | 8 cm |
| Min tank | 10 gal | 30 gal |
| Temperature | 24–30 °C | 21–28 °C |
| pH | 6–8 | 7–8.5 |
| Temperament | semi-aggressive | peaceful |
| Group size | 1 | 3+ |
Data from the Species Ledger, checked November 9, 2026, with at least two sources per species. Cautious community guidelines, not guarantees: individual fish vary. Not veterinary advice. Disagree? Tell us.