My CopperBand Butterfly ate mine. Had a couple rocks with quite a few patches and are now all gone. I saw him picking at them a number of times so I assume he is the reason for them disappearing.

I had a serious growth of hydroids and had tried everything to kill them with no success. One day last summer, my chiller broke and my tank went up to around 92 degrees. It killed all my sps and fish, but also killed my hydroids and they have never been back. I suggest you remove a piece of rock with hydroids from your tank and place it in a container and run the temp up to 92 degrees. It worked for me and it is worth testing on a small piece of rock.

Jim

similar to my running hot water over the affected area...
definitely effective.

Hammer & chisel, I did it. There are still some in my tank hidden away and at the bottom of 130lbs of rock so I don't try to get those but what I can get at relatively easy I hack away at.

Leave them alone, they will go away... or not. Hydroids are like algae, if you put something into the system that occupies their 'niche' or outcompetes them, they will recede and maybe even disappear. And as was said above, as reef tanks mature they seem to go through a bunch of stages where you are guaranteed to deal with algae, cyano, and a host of other nasty stuff... maybe this is something to be expected in our little tanks filled with incomplete ecosystems?

every tank is going to experience different "stages", what might have worked for you to just leave to sort itself out, might wind up an epidemic for someone else.
I can't agree that hydroids are like algae...they are a pest like algae, more like Aiptasia in that hydroids give a nasty sting to anything they touch (like your finger) and I have seen them kill a 5 inch sps overnight.

You should see how my red and gold zoas compete with my hydroids, it is incredible how much something can accelerate their reproduction in order to get the last word in their "niche".

I would deal with hydroids immediately if at all possible, wished I had when I had the chance.

Can you starve them?? IE stop feeding the tank or remove the rock and just let it be for a couple weeks?? I'm of the mind set you get them from over feeding but I may be wrong (again).

Douglas

I agree, best to deal with it immediately by removing as many as you can by whatever means necessary. What I'm saying is that for long term success, you need to find a way to remove whatever it is that they are feeding on that is causing them to grow out of control, be it nutrients or an imbalance of some kind.

And that's exactly what I meant, is that hydroids are like algae in the manner that they are pests and can easily get out of control... but I doubt hydroids occupy the same ecological niche as zoas. Are they mainly photosynthetic? I doubt it if they have stinging nematocysts, they probably feed on zooplankton or tiny 'pods.

I have had some in a basement cooking tank with no heat and no food going on 7 months...
There may be a lot of stuff in the water column in that tank though, so maybe a poor example.

Overfeeding will not cause hydroids, though it will contribute to their success in your tank.

And if you do a little dd on Hydroids, which are distant relatives of jellyfish you'll find that a common natural solution to get them gone is to put some zoas nearby, which will naturally try and outcompete the hydroids (and vice versa) for light and space.
If you don't think they sting, touch one.
I dare ya.:wink:

here's some reading to get you started.
http://www.wetwebmedia.com/hydrozoanfaqs.htm

I wouldn't use a blowtorch. The water within the live rock will turn to steam, then the rock will explode in your face.

I have a small patch of hydroids which not by coincidence is right under my feeding area. IME they grow with excess nutrients and recede when nutrient level go down.

I find the suction hose/filter sock in the sump trick while trimming the hyroids with scissors keeps them in check. I have some Aiptasia-X but I haven't tried it on my hydroids yet.