Can you help identify these ........... Critters?

[Frank Castle]

It should be fine, unless you're breeding as they can eat fry. You can get rind of them with salt, you can read this https://www.aquariacentral.com/forums/threads/should-i-be-concerned-about-hydra.82066/ for more info

exactly. I had them last year and left them alone and my fish ended up eradicating them. As long as there is no fry in the tank, they are not a threat