1. General Volume Calculation Rule

• The general rule: at least 1 liter of water is needed for every 1 cm of adult fish length.

• However, this applies only to small and peaceful species.

• Larger, more active, or aggressive species require significantly more space.

1. Aquarium Size Examples by Fish Species

• Guppy: Minimum 40–50 liters (suitable for 5–6 fish).

• Goldfish: At least 40 liters for one fish, +20 liters for each additional fish.

• Neon Tetra: A school aquarium of at least 60 liters (for groups of 10–12).

• Angelfish: Minimum 100 liters, as they can become aggressive as they grow.

• Betta: A 20-liter tank is enough for a single fish, but it must include a filter and heater.

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1. Other Factors Affecting Aquarium Size

• The size and maximum adult length of the fish.

• The species’ social structure (schooling fish or solitary?).

• Swimming space requirements (active swimmers need larger areas).

• The space taken up by plants, decorations, and equipment inside the tank.

• Filtration capacity and frequency of water changes.

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1. Disadvantages of Small Aquariums

• Water parameters deteriorate more quickly.

• Ammonia and nitrite levels rise more easily.

• Filtration and oxygen balance are more fragile.

• More challenging to maintain for beginners.

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1. Recommended Tank Size for Beginners

• At least 60–100 liters is recommended.

• This volume helps keep water parameters more stable and makes maintenance easier.

• Provides enough room for trying different species and using equipment.

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Conclusion
Choosing the right aquarium size is the foundation of creating a healthy habitat. Decisions should be based not only on the fish’s current size but also on its future growth, behavior, and species-specific needs. While larger aquariums may seem more costly at first, in the long run, they are more beneficial both for the fish and for easier maintenance.