Molly
Poecilia sphenops
Also known as Common Molly, Black Molly
Edited by Ivan F. · Reviewed
Beginner verdict
A peaceful, algae-grazing livebearer that needs hard, alkaline water to stay healthy. That water need matters more than anything else, and it is why mollies are not suited to a general soft-water community. In hard water they thrive, graze constantly, and breed with very little encouragement.
Care at a glance
- Min tank size
- 21 US gal
- Footprint
- 35 x 12 in
- Temperature
- 70–82 °F
- pH
- 7–8.5
- Hardness
- 15–30 dGH
- Swim zone
- Top
- Min group
- 3 fish
- Lifespan
- 3–5 years
Molly care mistakes to avoid
The mistakes beginners most often make with this species.
- Do not buy just one or two. Keep at least 3 fish so they feel secure.
- Only keep them in hard, alkaline water. Soft water leaves mollies prone to illness.
- Check tank mates share that hard water, as many tetras and rasboras do not.
- Expect fry. Keep more females than males to spread out the chasing.
- Check your tank before you buy. Our sourced minimum is 21 US gallons.
Molly tank mates and swim zone
Top
Spends most of its time in this part of the tank.
Hemigrammus erythrozonus
Danio rerio
Puntius titteya
Barbodes semifasciolatus
Corydoras aeneus
Corydoras aeneus (albino)
Danio margaritatus
Molly is much larger than Celestial Pearl Danio and may frighten or even eat it.
Tanichthys albonubes
Their temperature ranges barely overlap, so you will have little room for error.
Poecilia wingei
Endler's Livebearer is small and shy, and is easily outcompeted for food by Molly.
Betta splendens
Betta often does best alone. Only try this in a larger, planted tank, and watch closely.
Hyphessobrycon herbertaxelrodi
One needs much harder water than the other can tolerate.
Common tank-mate questions
Molly feeding and care
How to feed
- Feed flakes with plenty of vegetable content, because mollies graze on algae.
- Add blanched vegetables or frozen foods for variety.
- Feed small portions you can see finished within a couple of minutes, because overfeeding fouls the water fast.
Telling males from females
Males are smaller and more colorful, with a pointed anal fin called a gonopodium. Females are larger and rounder.
Plants that suit it
Species facts
- Family
- Poeciliidae
- Native to
- Mexico to Colombia
- Adult size
- 3.1 in (8 cm)
- Temperament
- Peaceful
- Social needs
- Harem/Pairs
- Diet
- Omnivore
- Water flow
- Gentle
- Substrate
- Any
- Live plants
- Mostly Safe
- Shrimp
- Adult Shrimp Only
- Fin nipping
- None
- Vulnerable to nippers
- No
- Breeding
- Easy Livebearer
Molly FAQ
What size tank do Mollies need?
Our sourced minimum is 21 US gallons (81 liters), with a footprint of 90 x 30 cm. A bigger tank is always easier to keep stable.
How many Mollies should I keep?
Keep at least 3 fish. Bigger groups usually look better and behave more confidently.
What can live with Mollies?
Good matches on our list include Glowlight Tetra, Zebra Danio and Cherry Barb. Avoid Neon Tetra and Cardinal Tetra.
How long do Mollies live?
Care guides report about 3–5 years. Stable water and a good diet make the biggest difference.
Do mollies need salt?
They need hard, alkaline water far more than salt. If your tap water is soft, consider a different species rather than trying to adjust your water.
Where to buy Molly
We have not found a store that sells Molly under its scientific name yet. We add stores as we confirm them.
Live animals and plants travel by courier. Check the store's live-arrival guarantee, and only buy once your tank has cycled (see how to cycle a fish tank).
Some US states restrict certain species. Check our US state aquarium rules table and your state's own rules before you buy.
Complete the tank
A forgiving setup with room for a small community.
Tank size for this species
At least 21 US gallons (81 L), 90 x 30 cm footprint
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.