How Many Mollies in a 30-Gallon Tank?

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Mollies are colorful, active, and peaceful freshwater fish that thrive in community aquariums.

They are also popular among beginners because they’re hardy and relatively easy to care for.

However, the most common mistake fish keepers make is overcrowding their tank.

If you’ve got a 30-gallon tank and are wondering how many mollies it can hold, you’re in the right place.

In this article, we’ll explain the ideal number of mollies for a 30-gallon tank, why tank size matters, and how to create the perfect environment for them.

How Many Mollies Can Live in a 30-Gallon Tank?

The simple answer: You can keep 8–10 mollies in a 30-gallon tank.

Why this number works:

  • Adult mollies grow 3–4.5 inches long.

  • They are social and prefer living in groups.

  • A 30-gallon tank provides enough swimming space and stable water conditions.

 Keeping 8–10 mollies ensures they have space to swim freely without stressing each other.

Why Tank Size Matters for Mollies

  • Active swimmers: Mollies love open swimming areas.

  • Social behavior: They prefer to live in small groups or schools.

  • Breeding habits: Mollies reproduce quickly, so extra space is essential.

  • Water stability: A bigger tank keeps water quality more stable.

Ideal Male-to-Female Ratio in a 30-Gallon Tank

  • 1 male for every 2–3 females is recommended.

  • This reduces aggression and stress caused by male mollies constantly chasing females.

  • Example: In a 30-gallon tank, keep 3 males and 7 females.

Best Setup for Mollies in a 30-Gallon Tank

  1. Filtration System – Choose a powerful filter that handles waste well.

  2. Live Plants – Provide hiding spaces and improve water quality.

  3. Water Parameters – Maintain 75–80°F temperature, pH 7.5–8.5.

  4. Tank Decorations – Add rocks, driftwood, or caves for natural hiding spots.

  5. Lighting – Moderate lighting keeps plants and mollies healthy.

Tankmates for Mollies in a 30-Gallon Tank

Good companions include:

  • Guppies

  • Platies

  • Swordtails

  • Corydoras catfish

  • Tetras

  • Snails

Avoid aggressive fish like cichlids, which may bully mollies.

Breeding Mollies in a 30-Gallon Tank

  • Mollies are livebearers and can give birth to 20–60 fry every month.

  • Use a breeding box or separate tank for fry to increase survival.

  • Provide floating plants like hornwort for hiding spaces.

Conclusion

In a 30-gallon tank, you can keep 8–10 mollies comfortably.

This setup allows them enough space to swim, reduces stress, and provides room for natural behavior.

If you want to enjoy the beauty of a lively molly community, a 30-gallon tank is a perfect size.

FAQs

1. Can I keep more than 10 mollies in a 30-gallon tank?
No, overcrowding leads to stress and water quality issues. Stick to 8–10.

2. How many male mollies can I keep?
Keep 1 male for every 2–3 females to maintain balance.

3. Can mollies live with goldfish in a 30-gallon tank?
No, because goldfish need cooler water while mollies prefer warmer water.

4. How often should I clean a 30-gallon tank with mollies?
Perform 25% water changes weekly and clean the filter regularly.

5. Do mollies need a heater in a 30-gallon tank?
Yes, mollies thrive in warm water between 75–80°F.

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