I had fry in the tank so I needed to get rid of the hydra before the fry became free swimming. so I researched online and found you can use panacur, the dog de wormer which fortunately I had on hand because I have to de parasite my imported fish before they can go in my community tank. 2 X 3cc vials liquid panancur per 55 gallons killed all hydra and not the fry.
