Help! Hydroids!

Just had hydroids appear for the second time in my life in a larval tank. I have no idea where they are coming from.  I haven't used brine shrimp in over a year.  i have several larval tanks that don't have hydroids, and this one that does.  I had been thinking that this particular tank was jinxed because I would successfully hatch eggs in it, and then next morning, all would be dead. Happened twice. I had a few lucky survivors, so I didn't immediately bleach the tank. A week later, I was looking at the rotifer density and there they were! 
 
Where could they be coming from? 

check out Kathy's Clowns, llc website:
http://kathysclowns.com
Captive bred clownfish and more
(Wholesale to the trade.)

Ah, did some reading on hydroids.  The non medusa stage is an anemone like stage that is growing profusely in one of my broodstock tanks.  So that's where they are coming from, and explains quite a lot.  I know i ordered panacur some time ago, but for the life of me, I can't find it now….
 

check out Kathy's Clowns, llc website:
http://kathysclowns.com
Captive bred clownfish and more
(Wholesale to the trade.)

I was thinking, from what you said, that a broodstock tank was the most likely vector.  Just remember Panacur's effect on snails in tanks that have been treated with it, reportedly for even years after the fact.

Luckily, I have no snails.  I have thousands of bristle worms, though, and lots of live rock, so if I treat with panacur, it will be a mess to remove all the dead bodies.  I think I have hydroids in both brood stock systems.  sigh. Nothing like starting over.

check out Kathy's Clowns, llc website:
http://kathysclowns.com
Captive bred clownfish and more
(Wholesale to the trade.)

Panacur will kill any snails that are herbivores but usually not the carnivores.  Omnivores will suffer as well.  It also wreaks havoc on the bristle worms but doesn't completely kill them all.
 
The liquid version doesn't have the long lasting effect that the granules does.
 
Dan

I ordered some from you, Dan.  Thanks for the info.

check out Kathy's Clowns, llc website:
http://kathysclowns.com
Captive bred clownfish and more
(Wholesale to the trade.)

Thanks for the info Dan!  I recently got some Fenbendazole to treat my broodstock system, but I'm hesitant simply because the thought of using a medication I've never used before on all my broodstock freaks me out!  Good to know the liquid isn't so long lasting.
 
Good luck Kathy!

Don't let fear and common sense stop you! =]