How to Kill Hydra in a Freshwater Aquarium
Hydra are related to jellyfish and are a common pest in home aquariums. Hydra are not generally harmful to fish, except they do have the ability to catch and consume small fry and shrimplets. Hydra are usually an indication of overfeeding, so feeding smaller quantities less often will help put a dent in their populations but their populations can be knocked out completely with a dose of common dog dewormer, available over the counter called Fenbendazole. Dose 0.1g fenbendazole per 10g of water volume. For heavy infestations, monitor water quality carefully after treatment to monitor for harmful ammonia spikes from decaying hydra.