Mollies are among the most popular freshwater aquarium fish thanks to their bright colors, playful nature, and easy care requirements.
However, one of the biggest mistakes new fish keepers make is overcrowding a small tank.
A 5-gallon tank may look cute and easy to manage, but it raises the important question: How many mollies can live in a 5-gallon tank?
In this article, we’ll break down the ideal number, explain why tank size matters, and give you tips to keep mollies happy and healthy in smaller setups.
How Many Mollies Can Live in a 5-Gallon Tank?
The short answer: Only 1 molly fish can live comfortably in a 5-gallon tank.
Here’s why:
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Adult mollies grow up to 3–4.5 inches long.
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They are active swimmers that need open space.
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A 5-gallon tank is considered “nano” size, better suited for shrimp, snails, or a single betta.
Keeping more than 1 molly in a 5-gallon tank leads to overcrowding, stress, and poor water quality.
Why a 5-Gallon Tank is Too Small for Multiple Mollies
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Limited swimming space: Mollies are social and active. A cramped tank restricts movement.
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Water quality issues: Waste builds up quickly in small tanks, leading to ammonia spikes.
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Aggression risk: Males can become territorial, especially in tight spaces.
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Breeding problems: Mollies reproduce rapidly, and fry have no room in a 5-gallon tank.
Best Setup for a Single Molly in a 5-Gallon Tank
If you decide to keep 1 molly in a 5-gallon aquarium:
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Use a good filter – Small tanks need efficient filtration.
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Add live plants – Plants improve water quality and give hiding spots.
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Maintain stable water – Temperature should be 75–80°F with a pH of 7.5–8.5.
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Perform frequent water changes – Replace 25–30% weekly to keep parameters stable.
Better Alternatives for Mollies
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10-gallon tank – Suitable for 2–3 mollies.
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20-gallon tank – Perfect for 4–5 mollies.
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30+ gallon tank – Great for a larger group or community tank.
If you love mollies and want to see their natural schooling behavior, aim for at least a 20-gallon setup.
Conclusion
In a 5-gallon tank, you should only keep one molly fish.
While it’s tempting to add more, doing so risks the health and happiness of your mollies.
If you plan to keep a group, consider upgrading to a larger tank where they can thrive.
FAQs
1. Can I keep 2 mollies in a 5-gallon tank?
No, it will overcrowd the tank. Stick to 1 molly.
2. Can mollies breed in a 5-gallon tank?
Yes, but it’s not recommended since fry will have no space and water quality will suffer.
3. What fish can live with a molly in a 5-gallon tank?
None. The tank is too small for tankmates.
4. Are 5-gallon tanks good for beginners?
They are harder to maintain because water parameters fluctuate quickly.
5. Should I upgrade if I want more mollies?
Yes, a 20-gallon tank or larger is much better for multiple mollies.