There are a few species of fish that ravenously eat hydra including Blue Gouramis, Mollies and Paradise fish. Pond snails also feed on hydra when they are placed in the aquarium environment.
Hydra are an aquatic organism found in aquariums, and they typically originate from an exterior source. Unfortunately, hydra often become difficult to manage inside of fish tanks as they reproduce rapidly, and many tank owners struggle to find the right method of getting rid of them. There are, though, proven methods of preventing hydra from taking over an aquarium including keeping the tank very clean and avoiding overfeeding fish.