We can get flubendazole, here, from some veterinarians, and it is a sure cure for Hydra.
If you cannot get it, dosing with Formalin (37% formaldehyde) every other day for three doses usually kills them off, without harming the plants or fish.
I vaguely recall it was about 3 drops per 5G, but I'm not sure since it has been a long time since I had the problem. Repeat dosing is mandatory as the formaldehyde is absorbed by organic mulm within a day or two. I find it takes at least three treatments to be effective. Don't do any water changes until it is finished. The first treatment makes them retract into a lump. They come back out the second day, so hit them again. By the third treatment they should be dead. If not, repeat, using a stronger dose.
Since Formalin is carcinogenic and produces harmful fumes, you can get almost the same effect by using one of the better dechloraminators, like Amquel or Prime, at somewhat above the normal doses. [Note that dechlorinators will not have any effect. They are the ones that advertise that they "break the chlorine ammonia bond." Use the kind that binds the ammonium.]
Do remove all snails, shrimp, and other inverts before treating for Hydra, as the things that kill Hydra can do a lot of damage to them. Also, you will kill all infusoria, so the water will be unsuitable for raising babies. Don't feed bbs or other small live foods during treatment. They will die quickly and foul the water.
Copper sulfate also kills Hydra, but does a number on plants and fish, too. I don't like it, and never use it, any more.
I like natural cures, so adding Trichogaster-type Gouramis is a good way to get rid of them (they love to eat Hydra), as is withdrawing all live foods for a week or so. Hydra can only survive with a constant supply of living foods.
They are a lot easier to treat than really harmful pests, like flatworms that devour eggs.
Wright
01 760 872-3995
805 Valley West Circle
Bishop, CA 93514 USA
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