A section of Bushmans water tank calculator. Water Tank Sizes for Different Family Sizes. The appropriate water tank size for a household depends on several factors, including the number of people in the household, average daily water usage, and frequency of rainfall.
It's not just about swimming space but about water quality and it would be very difficult to provide consistently good water quality in a 30 litre tank. I would suggest 45 litres as the absolute minimum for keeping fish, and then you'd be looking at a single betta or something similar.
Water Quality: Larger tanks are inherently more stable in terms of water parameters.They require a minimum tank size of 75 gallons, and prefer a long tank over a tall one. They also need a secure lid, as they are known to jump. Tank Setup and Environmental Considerations.

Water Quality: Larger tanks are generally more stable and easier to maintain good water quality in. The more the water there is, the more stable the temperature and pH balance will be. Filtration Capacity: Effective filtration is essential, but its not a substitute for adequate tank size.
And a 180cm tank is really the minimum for Frontosa.

As we can see from the illustration, Minimum Tank Size For Good Water Quality has many fascinating aspects to explore.
The absolute minimum tank size for a small group of guppies (3-5) is 5 gallons, but a 10-gallon tank is highly recommended as it provides more stable water parameters and room for the guppies to thrive and breed comfortably. The Allure of Guppies: A Popular Choice for Aquarium Keepers.
Angelfish require good water quality, with zero ammonia or nitrite in the water. They prefer water with a slightly acidic to neutral pH, between 6.5 and 7.8.Care Level: Easy. Diet: Carnivore. Minimum tank size: 20 gallons. Origin: Brazil, Suriname & Guyana. Swimming Level: Mid-water.

Furthermore, visual representations like the one above help us fully grasp the concept of Minimum Tank Size For Good Water Quality.
They need clean, stable water to stay healthy. If you can maintain good water quality and keep them in a proper group, they become one of the most active and visually impressive fish in a community tank.Minimum Tank Size.