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I'm just back from seven long weeks away from by beloved tanks, and i find the little tank swarming with hydras. What is a hydra; friend or foe? How do i get rid of them (assuming i need to..? ) How did they get there in the first place?

nim

Hydra will not harm your fish and are only dangerous to eggs and fry. All kinds of treatments have been proposed: copper sulphate, ammonium nitrate, stopping of live foods, raising the temperature to 40°C for short periods, even introducing a weak electric current. However, the most effective way to get rid of Hydra is to use either flubendazol or fenbendazol. Dactycid also works, but I'm not sure if it's available to you.

Hi and Thanks.

Unfortunately, however the hydras are in the egg & fry tank, so i suspect they'll need to go, unless i could move them to the bigger tank. Is there a non-chemical way to remove them? - as there are no fish currently in the tank could i try hot/boiling water? I've read that they have stinging tentacles so i figure they are probably not ideal fish food... and any idea what conditions triggered them?

thanks again, nim

If there are no eggs/fry in the tank, you can either starve them out, or use hot water.

The best way -next to starving them that is- to rid the tank is get a temporary guest; a Blue Gourami (Trichogaster trichopterus) or a similar fish. they eat the things!

another way, but only if no fish reside in there, is adding a few stripped copper wires in there; you can connect them with a flashlight battery (NOT the juice outlet in the wall!!!) and run that battery empty.
the Hydra's will presish.
Afterwards it's quite easy to mop up the copper-ions, by using a new batch of activated carbon followed by a few rigorous waterchanges and by using a good tonic on the last one. (this will neutralize leftover copper)

Using fresh activated carbon to starve out Hydra's is also good, in combination with waterchanges. It makes the water "poor" on certain substances infusoria (microscopic organisms) need to thrive. Without those substances, no infusoria. Without infusoria, the hydra's will starve...


Blue Gourami

Best way to use a Blue Gourami, is buying one or more (they're dirtcheap! and peaceful too), feed them for a few days to get them used to the tank and then stop feeding for a week or so. That way they'll eradicate the Hydra's, otherwise they get lazy. And use only flake food; Hydra's don't do well on flake.

Well the holocaust is over now, though i think i have a little black mark in the 'karmic debt' section of my score card..
Thanks for all the suggestions; in the end hot water seemed the simplest method, and for future reference, it worked wonders.

nim