re: getting rid of Hydra (just in case this info is useful) …
I had green Hydra in my Hyallela tank and can report that I got rid of them using NT Labs Anti-Fluke and Wormer. The active ingredient is flubendazole, as in many other antihelmintic preparations. This one is convenient, though, because the flubendazole is pre-dissolved (it dissolves extremely reluctantly in water).
I rescued as many Hyallela as I could and parked them in temporary accommodation while I treated their tank. The day after the first dose I inspected the tank. At first it appeared that all the Hydra had gone but I did eventually find three that seemed still operational (I poked them with a skewer and they collapsed!). So I applied a second dose, after which I haven’t seen any Hydra at all in that tank. Incidentally, the Hyallela that remained in the tank during treatment all survived it.
I now have to deal with an outbreak of Hydra in my blackworm tank, which might be more problematic!