Mollies are popular livebearers that come in many colors and fin shapes.
They’re hardy, active, and easy to care for, making them a favorite among aquarium enthusiasts.
But if you’re setting up a 10-gallon tank, how many mollies can it safely hold?
Let’s find out.
Molly Fish Basics
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Average Size: 3–4.5 inches (some breeds grow larger)
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Temperament: Peaceful, social, but can get territorial in small tanks
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Breeding: Livebearers, reproduce quickly
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Lifespan: 3–5 years with good care
How Many Mollies in a 10-Gallon Tank?
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General Rule of Thumb: 1 inch of fish per gallon.
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Since mollies grow up to 3–4 inches, a 10-gallon tank can house:
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3–4 mollies maximum (depending on size and type).
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For better balance, 3 mollies is ideal.
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Overcrowding should be avoided, especially if breeding.
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Best Stocking Choice: 3 mollies in a 10-gallon tank.
Why a 10-Gallon Tank Is Small for Mollies
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Mollies are larger than guppies and tetras.
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A small tank may cause stress and aggression.
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Fry from breeding will overcrowd the aquarium quickly.
Tank Setup Tips for a 10-Gallon Molly Tank
Filtration
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Use a filter rated for 15–20 gallons.
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Mollies produce a lot of waste, so strong filtration is important.
Substrate & Décor
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Sand or fine gravel works well.
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Add live plants like java fern, hornwort, and anubias.
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Leave open swimming areas, as mollies are active fish.
Water Conditions
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Temperature: 75–82°F
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pH: 7.5–8.5 (slightly alkaline water preferred)
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Weekly 30% water changes are recommended.
Pros of a 10-Gallon Molly Tank
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Affordable and easy to set up.
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Suitable for beginners with proper care.
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Can house a small group of mollies for enjoyment.
Cons of a 10-Gallon Molly Tank
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Limited space—mollies usually do better in 20+ gallon tanks.
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Breeding will overcrowd quickly.
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More frequent maintenance is required to maintain water quality.
Conclusion
A 10-gallon tank can safely house 3 mollies, but it’s not ideal for larger groups.
If you want a thriving molly community or plan on breeding, consider upgrading to a 20-gallon or larger aquarium.
FAQs
1. Can I keep 5 mollies in a 10-gallon tank?
No, that would be overcrowded. Stick to 3 mollies maximum.
2. Do mollies need a heater in a 10-gallon tank?
Yes, they require warm, stable temperatures to stay healthy.
3. Can I keep mollies with other fish in a 10-gallon tank?
Not recommended, as mollies need most of the space.
4. Will mollies breed in a 10-gallon tank?
Yes, but fry will quickly overcrowd such a small tank.
5. What’s the ideal tank size for mollies?
A 20–30 gallon tank is best for a larger group.