5-10 guppies can be raised in a 20 cm fish tank. Although guppies are not very big, their body length can reach 4-6 cm when they grow up. If the fish tank is not large, their activities will be limited, so the number of aquaculture should not be large, otherwise there may be fights and their growth and development may be affected. Under normal circumstances, it is most appropriate to raise 5 guppies in a 20 cm fish tank. If it is a guppy in its infancy, it will be smaller in size and raise more, about 10 of which can be raised.

It is not good to raise guppies in small tanks. First of all, if the space in fish tanks is insufficient, their daily activities will be affected, and over time, their body shape will be stunted. Secondly, the fish tank is too small, and the water in the fish tank will not be much, which will easily be polluted, resulting in poor water quality.

Guppies are sensitive to the fluctuation of water quality, and breeders can't change water frequently to keep the water clean. Finally, the small tank is prone to lack of oxygen, because the fish tank is small and the water body is very small. It is easy to have a lack of oxygen. If the breeder can't keep the frequency of changing water, there will often be lack of oxygen in the fish tank.