Are hydra bad for aquariums?
Hydra are ambush hunters that like to eat microworms, insect larvae, and tiny crustaceans (e.g., cyclops, daphnia, scuds, and baby brine shrimp). In our experience, they are a natural part of the aquarium ecosystem and do not seem to greatly impact baby fish and shrimp populations. Adults are too big to be eaten, and fry have a strong flight response that causes them to jerk away from any stimulus, like a stinging tentacle.
For more information, read our full article on How to Get Rid of Hydra in Your Aquarium.