Digitate Hydroids

[Gtinnel]

So I just looked at my tank shortly after the lights went out and I noticed that I have more digitate hydroids than I realized. To be fair I knew I had a few but they never caused any issue so I didn't worry about them too much. I've been feeding more frequently to keep my nitrates detectable and I suspect that has aided in their growth. It's still not an alarming amount but more than I'd care to have.

I've been reading online about them and all of the information I am seeing seems to be very mixed. From they're harmless and will eventually fade, to they will take over the tank and kill everything and eventually murder me while I sleep. A lot of the information I've been reading seems to mix up digitate hydroids and colonial hydroids making it even more frustrating to find reliable information. Does anyone know of a predator that will eat digitate hydroids? One place said foxfaces may but I think they were talking about colonial hydroids. Then somewhere else said Halloween hermits crabs would.

What would be your approach to kill off, or at least limit the population, of digitate hydroids, without using the chemical method? I don't have anywhere near enough to use chemicals.

 

[Nano sapiens]

So I just looked at my tank shortly after the lights went out and I noticed that I have more digitate hydroids than I realized. To be fair I knew I had a few but they never caused any issue so I didn't worry about them too much. I've been feeding more frequently to keep my nitrates detectable and I suspect that has aided in their growth. It's still not an alarming amount but more than I'd care to have.

I've been reading online about them and all of the information I am seeing seems to be very mixed. From they're harmless and will eventually fade, to they will take over the tank and kill everything and eventually murder me while I sleep. A lot of the information I've been reading seems to mix up digitate hydroids and colonial hydroids making it even more frustrating to find reliable information. Does anyone know of a predator that will eat digitate hydroids? One place said foxfaces may but I think they were talking about colonial hydroids. Then somewhere else said Halloween hermits crabs would.

What would be your approach to kill off, or at least limit the population, of digitate hydroids, without using the chemical method? I don't have anywhere near enough to use chemicals.

Pesky little things, aren't they? Here's what I've observed and how I handle them:

First thing is that there are actually quite a few digitate hydroid species. Apparently some have a rather mild sting (that's why some people say they do little or no harm even near coral), but some like the ones I have have a very potent sting.

I've been manually removing for the last few months any that I can get to the base using a surgical style tweezer. I can nearly eradicate them, but in a week or two I'll start to see new young ones pop up, plus a few large oldies that I missed or couldn't get to. Any that I can't get to the base I'll grab the thread with the tweezer and carefully stretch it like a rubber band for 20-30 s. This makes it impossible for them to retract properly and I can then easily remove most of the thread. They can regrow and come back once or twice in the same location, but then they'll often move once treated this way and then hopefully their base can be seen and the animal carefully removed (best not to break them into floating pieces, if possible).

I have a Halloween Hermit and it's in a 12g, but to date I haven't seen it eat a digitate hydroid (it will eat old tubes of colonial hydroids, but no young ones). So, some *may* eat DH, but mine looks like it doesn't.

The best control to date (besides tweezering them) is not to feed small food like ReefRoids and first rinse Mysid and such in a net before feeding to limit small particles. I had hoped that would be enough since they should run out of in-tank pods and such, but they seem to get by on very little food. At least with these measures their reproduction rate is slow enough for me to keep up with.

For me, it's now about control vs. complete eradication (if I can't get rid of them in a 12g, I can imagine how hard it would be without chemicals in something like a 150g!). Any that get into my Zoas I have to immediately deal with or else in a few days permanent damage will be done. SPS encrusters are less effected since while they get damaged, it's generally localized and the rest of colony continues to grow and does fine.

 

[EFlop]

Was reading another thread about powdered food and broadcast feeding being a potential cause. I looked into mine tonight and saw at least a couple different types of hydroids getting too comfy with my micro lords.

 

[Nano sapiens]

Was reading another thread about powdered food and broadcast feeding being a potential cause. I looked into mine tonight and saw at least a couple different types of hydroids getting too comfy with my micro lords.

I've had a few try to move in with my Micromussa. Interestingly, they don't tend to stay there long and it may be due to the large polyps interfering with their flippy-floppy feeding method. They just love zoa colonies, though!

 

[Gtinnel]

Pesky little things, aren't they? Here's what I've observed and how I handle them:

First thing is that there are actually quite a few digitate hydroid species. Apparently some have a rather mild sting (that's why some people say they do little or no harm even near coral), but some like the ones I have have a very potent sting.

I've been manually removing for the last few months any that I can get to the base using a surgical style tweezer. I can nearly eradicate them, but in a week or two I'll start to see new young ones pop up, plus a few large oldies that I missed or couldn't get to. Any that I can't get to the base I'll grab the thread with the tweezer and carefully stretch it like a rubber band for 20-30 s. This makes it impossible for them to retract properly and I can then easily remove most of the thread. They can regrow and come back once or twice in the same location, but then they'll often move once treated this way and then hopefully their base can be seen and the animal carefully removed (best not to break them into floating pieces, if possible).

I have a Halloween Hermit and it's in a 12g, but to date I haven't seen it eat a digitate hydroid (it will eat old tubes of colonial hydroids, but no young ones). So, some *may* eat DH, but mine looks like it doesn't.

The best control to date (besides tweezering them) is not to feed small food like ReefRoids and first rinse Mysid and such in a net before feeding to limit small particles. I had hoped that would be enough since they should run out of in-tank pods and such, but they seem to get by on very little food. At least with these measures their reproduction rate is slow enough for me to keep up with.

For me, it's now about control vs. complete eradication (if I can't get rid of them in a 12g, I can imagine how hard it would be without chemicals in something like a 150g!). Any that get into my Zoas I have to immediately deal with or else in a few days permanent damage will be done. SPS encrusters are less effected since while they get damaged, it's generally localized and the rest of colony continues to grow and does fine.

The only effect that I have seen on my corals is I have one near a frag of rasta zoas and it touches one single polyp causing it to stay closed. The polyp will open if not being touched for a while so I suspect my hydroids do not have a particularly strong sting. Most of the hydroids I saw were actually attached to the bottom of my frag rack, so I can easily kill them by removing that frag rack. I guess for the others I will just work on manual removal. I should probably figure out a way to get some form of mechanical filtration too. Right now my sump doesn't have any, and honestly no space to easily add any.
I've also seen someone else post that ruby mithrax crabs may kill them, has anyone else experienced this. I'm leery of adding one because I had an emerald crab once that started eating corals.