To solve problems that conventional filtration equipment is not easy to clean and exchange a filter layer, to occur water leakage and affects the environment for growing organisms caused by deflection in biological filtration as it is composed of a single unit, while closed filtration equipment are also not easy to clean and exchange filtering materials.

This filtration equipment for growing aquatic organism is capable of easily installing and removing the filter layer by combining a filter layer- installing case, the filter layer and its associated water discharging device and connecting the devices in numbers required for treating water. Thus, even when one of plural filter cases is exchanged for cleaning during maintenance, filtration in other filter layers functions stably owing to the connection of the filter cases. The aquatic organism growing water tank by using the filter case is also provided.