Molly

Poecilia sphenops

Also known as: Common molly, Black molly, Short-finned molly

Water Parameters

• Temperature: 24–28°C
• pH: 7.5–8.4
• Hardness (GH): 179–536 ppm (10–30 dGH)

Values above are general hardness (GH). For carbonate hardness (KH), the buffer that keeps pH stable, see the water parameters guide.

Care Summary

A robust livebearer sold in solid black, dalmatian, silver, and gold, as well as lyretail and sailfin finnage variants. Females are larger than males and produce broods of 20 to 60 fry roughly monthly. Mollies are frequently described as easy beginner fish, which is only half true: they are hardy and forgiving of handling, but unforgiving of soft water and poor water quality, and are prone to the shimmies, a swaying, going-nowhere swimming motion that signals stress, chill, or unsuitable water chemistry. In the hard, alkaline tap water common across much of Australia they are genuinely straightforward. A strong choice where guppies feel too small and delicate. A big part of that is buffering: a moderate to high carbonate hardness (KH) keeps the pH stable and above 7.5, which is what mollies actually need, so do not let it fall to soft, low-KH levels.

Tankmates

A peaceful, sociable livebearer best kept in groups with more females than males. Larger and more substantial than guppies, with a healthy appetite for algae that makes them useful as well as decorative. They require hard, alkaline, mineral-rich water: this is the single most common reason mollies fail, as keepers place them in the soft, acidic conditions that suit tetras and rasboras. For that reason they are a poor match for soft-water species. Mollies are notably salt-tolerant and are sometimes kept in low-end brackish setups, though this is optional in suitably hard fresh water.

Compatible with

• Platy
• Swordtail
• Guppy
• Bronze Corydoras
• Bristlenose Pleco
• Nerite Snail
• Mystery Snail

Avoid keeping with

• Betta
• Neon Tetra
• Tiger Barb
• Fin Nippers
• Large Cichlids

Common Problems

• the shimmies from soft water or chills
• sensitivity to poor water quality
• overpopulation from breeding
• ich
• fin rot

Sources: seriouslyfish.com, fishbase.org · Last updated: 2026-06-20