Molly
Poecilia sphenops
beginner careOverview
The molly (Poecilia sphenops) is a hardy, sociable livebearer that comes in black, silver, dalmatian, gold and sailfin forms. Larger and bulkier than guppies, mollies are peaceful grazers that spend the day picking at algae and browsing the tank. They are easy and beginner-friendly, with two things to plan for: their taste for hard, mineral-rich water, and their prolific breeding.
Tank & water
Mollies are bigger and messier than they look, so give a small group at least 75 litres (20 gallons) with strong filtration.
- Temperature: 24–28 °C, held with a heater.
- Water: hard and alkaline, pH 7.5–8.5; they appreciate high mineral content and tolerate brackish conditions, though salt is not essential.
- Filtration: a good filter is important — mollies produce a lot of waste and enjoy some flow.
- Planted and open: they graze on plants and surfaces but also need open swimming space.
Feeding
Mollies are omnivores that lean herbivorous, so vegetable matter is important. Use a quality flake or pellet with a good plant content — spirulina and algae-based foods are ideal — plus blanched vegetables and occasional frozen or live protein such as brine shrimp and daphnia. Their natural grazing on algae is a bonus, not a complete diet.
Tankmates
Peaceful and easy-going, mollies mix well with other hard-water community fish: platies, swordtails, guppies, larger tetras and peaceful catfish. Avoid fin-nippers and aggressive fish. Because mollies are larger, keep smaller nano fish only if they aren’t small enough to be seen as food.
Given hard water, room and good filtration, the molly is a characterful, hardy addition to a cycled community tank.
Molly — frequently asked questions
Do mollies need hard water or salt?
Mollies do best in hard, alkaline water (pH 7.5–8.5) and appreciate a higher mineral content than most community fish. They can be kept in brackish water and some keepers use a little aquarium salt, but pure fresh water is fine as long as it is hard — salt is optional, not required.
Why is my tank full of baby mollies?
Mollies are prolific livebearers, and a mixed group produces broods of fry every few weeks. Keep more females than males, or a single sex, and plan for the population — otherwise numbers climb quickly.
How big do mollies get and what tank do they need?
Depending on the variety, mollies reach 6–10 cm and are surprisingly bulky, so give a group at least 75 litres. They are active, messy fish that need swimming room and good filtration.
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