How to Kill Freshwater Hydra

Vacuum the aquarium. Sweep the bottom of the tank with the vacuum to remove the hydra and a majority of their food sources. Use the aquarium vacuum as needed to keep the freshwater aquarium clean. This will prevent more hydra from appearing in your aquarium.

Replace any lost water. Vacuuming the aquarium will pull out a fair amount of water. Replenish the aquarium with additional freshwater. Northern State University suggests using freshly collected pond water or rain water.

Reduce the amount of food you feed the fish in the tank. Temporarily decreasing the amount of food will result in larger fish feeding on the hydra and eliminating a source of food for the hydra. If food is unavailable, hydra reproduction will cease and they will eventually shrink then die.

Repeat these steps as necessary. Continue the three-step process until all signs of hydra are gone. Negligence in cleaning the tank or feeding the fish ample amounts will allow the hydra to feed as well, and thus rapidly reproduce. Continuing the steps is also a maintenance measure that will prevent additional hydra from developing in your freshwater aquarium.