| Temperature | 24–28 °C (75–82 °F) |
|---|---|
| pH | 7.5–8.5 |
| Min tank | 20 gal (76 L) |
| Adult size | 10 cm |
| Lifespan | 3–5 years |
A Molly is one of those animals that looks simple in the shop bag and turns out to have opinions once it is home. The Poecilia sphenops Molly is a long-time favourite for a reason, but it has specific needs that generic "community fish" advice misses.
At a glance
| Minimum tank | 20 gallons (76 L) |
|---|---|
| Temperature | 24 to 28 °C |
| pH range | 7.5 to 8.5 |
| Adult size | 8 to 10 cm |
| Lifespan | 3 to 5 years |
| Group size | a group of 6+ |
Where it comes from
In the wild the Molly lives in slow, vegetated waters where cover is everywhere and currents stay gentle. Recreating that means planting densely, keeping the filter flow soft, and avoiding bright, open tanks that leave the fish exposed. Stable water matters more than perfect parameters.
Tank setup
Start with at least 20 gallons and a mature, cycled filter — see the 20-gallon setup guide before you buy. A sand or fine gravel substrate, a few driftwood branches and a carpet or mid-ground plant mass give the fish somewhere to retreat. Keep nitrates under 20 ppm with a weekly 23% water change.
Feeding
Feed a varied diet: a quality flake or micro-pellet as the base, topped up with frozen or live foods two or three times a week. Offer only what the fish clears in about 1 minutes, once or twice daily. Overfeeding is the single most common cause of water-quality swings.
A mistake everyone makes
Adding a Molly to a brand-new tank is the classic error. An uncycled tank spikes ammonia to 1.1 ppm within days and the fish pays for it. Cycle first, stock lightly, and let the group size build up gradually.
Good tank mates
Peaceful, similar-sized neighbours work best. Avoid fin-nippers and anything large enough to swallow the Molly. A planted community with the co2 system for a large tank in the mix tends to settle quickly.
Community tank mates
The Molly does best with peaceful, similar-sized neighbours and away from fin-nippers or anything large enough to eat it. A group of 6+ stays calm, and mixing it with other community fish keeps aggression low.
