Molly Fish Care Guide
Everything you need to know about keeping mollies healthy and breeding successfully. From black mollies to sailfins, learn why hard water and salt make the difference.
Tank Size Requirements
Prolific breeders alert
Mollies are livebearers that breed readily. A single female can produce 20-100 fry every 4-6 weeks. Plan for population growth or keep single-sex groups.
Minimum Requirements
- Minimum: 10 gallons for a small group
- Recommended: 20+ gallons for comfort and breeding
- Sailfin Mollies: 30+ gallons (they grow larger, up to 6")
- Heater: Required for stable tropical temperatures
- Filter: Moderate flow, mollies produce moderate waste
- Plants: Live plants appreciated for grazing and fry cover
Mollies are active swimmers that use all levels of the tank. A longer tank is better than a tall one. Keep at least 3 mollies together, with a 2:1 female to male ratio to prevent harassment.
Ideal Water Parameters
Salt: Optional But Beneficial
Mollies naturally occur in brackish waters and tolerate (even thrive with) some salt. Adding 1 tablespoon of aquarium salt per 5 gallons can prevent "shimmies" and boost immunity. However, this makes them incompatible with salt-sensitive tank mates like corydoras and many plants. Full marine salt is not needed; regular aquarium salt works.
Diet & Feeding
Mollies are omnivores with a strong preference for plant matter. In the wild, they graze constantly on algae. A high-vegetable diet keeps them healthy and colorful.
Recommended Foods
- Staple: High-quality flake or pellet food with spirulina
- Vegetables: Blanched zucchini, cucumber, spinach, peas
- Algae: Algae wafers, let some tank algae grow for grazing
- Protein: Occasional bloodworms, brine shrimp (1-2x weekly)
Feeding Schedule
- Amount: What they can consume in 2-3 minutes, 2-3 times daily
- Grazing: Mollies prefer to eat small amounts throughout the day
- Vegetables: Offer blanched veggies 2-3 times per week
- Pregnant females: Feed more frequently with protein-rich foods
Tank Mate Compatibility
Mollies need hard, alkaline water. Avoid tank mates that require soft, acidic conditions. If adding salt, only keep salt-tolerant species together.
Common Diseases & Treatment
Molly Disease (Shimmies)
Rocking motion, clamped fins, difficulty swimming, staying in place
Mineral deficiency, cold water, soft water, lack of salt
Add aquarium salt (1 tbsp/5 gal), raise temp, improve water quality
Ich (White Spot)
Small white spots on body. Scratching against objects.
Rx: Raise temp to 82°F + aquarium salt + ich medication
Fin Rot
Ragged, discolored fins that appear to be deteriorating. Often starts at edges.
Rx: Clean water, aquarium salt, antibacterial medication if severe
Velvet
Gold or rust-colored dust on body, lethargy, rapid breathing. Parasitic infection (Oodinium).
Hard water prevents most molly problems
The majority of molly health issues stem from keeping them in soft, acidic water. Ensure your water is hard (15+ dGH) and slightly alkaline. Adding aquarium salt provides an extra layer of disease prevention.
Related Resources
Track Your Mollies' Health
MyAquaLog helps you monitor water hardness, track breeding, and catch problems early. Log births, track fry growth, and ensure your colony thrives.
Start Tracking Free