Free swimming hydroids are still multiplying

Nooonan · Mar 23, 2017

One of my systems is a relatively young 60 gallon seahorse/macro algae tank. The tank has a pair of captive bred hippocampus reidi, a designer ocellaris, gorgs, and the sand bed is completely covered with caulerpa prolifera.

About 3 weeks ago I was doing a water change and I was using my gravel vac to clean up inside the caulerpa bed. After stopping the siphon I continued to work around the tank and happened to see something out of the corner of my eye. I honestly thought at first that the water was boiling in one corner of the tank, but this was just because of the activity of a few thousand tiny jellyfish looking creatures. I didn't have a problem before this point.

I'm well aware of what they are and I know that they aren't an issue for larger species of seahorses. They're continuing to multiply and they're population is getting out of control. These hydroids have got to be annoying for the seahorses/clown, You literally cannot look at the tank and find a few square inches of open water where they are not swimming. I have shut down all flow, let the tank settle for a minute and siphoned them out. It helps until the next day, and then it doesn't seem like I did absolutely anything. I am considering siphoning out the tank into filter cotton and pumping it back in and continuing this progress to filter them from the water BUT the filter on the tank doesn't seem to help reduce their population at all.

What else can I do? I've heard peppermint shrimp MAY take care of them just like they MAY take care of aiptasia. I've also heard Flatworm Exit could kill them but I haven't found many other sources to back that up.

Any advice is appreciated.

Lionfish Lair · Mar 23, 2017

I've never known them to be irritating and I've seen them on horses like pimples on a teenager. They will let you know if they're irritated. If you don't see it, they are not.

Nooonan · Mar 23, 2017

I was hoping you'd chime in, thanks for the fast response as always.

I've never actually seen them attached to the seahorses so that makes me feel a little better..

These will eventually die off, correct? How long can I expect that to take?

Lionfish Lair · Mar 23, 2017

One time I had them for a long time. I think it's because that tank had a crazy amount of diatoms at its initial start up.

I remember a seahorse had one on his eyeball and he was looking around with this little guy attached. It was kind of funny. They were constantly getting in the fry tank and they were THICK with them. I had to siphon them out daily to keep the numbers down. I ASSUME I was told correctly back then that they could harm fry, but to be honest, I don't know if that's a real fact or not, now that I'm sitting here thinking about it. I need to check the source of that. Are you dosing your tank with anything? Feeding your gorgs small particulate foods? Phyto? Do you have any residual diatoms?

Nooonan · Mar 24, 2017

Lionfish Lair said:
One time I had them for a long time. I think it's because that tank had a crazy amount of diatoms at its initial start up.

I remember a seahorse had one on his eyeball and he was looking around with this little guy attached. It was kind of funny. They were constantly getting in the fry tank and they were THICK with them. I had to siphon them out daily to keep the numbers down. I ASSUME I was told correctly back then that they could harm fry, but to be honest, I don't know if that's a real fact or not, now that I'm sitting here thinking about it. I need to check the source of that. Are you dosing your tank with anything? Feeding your gorgs small particulate foods? Phyto? Do you have any residual diatoms?

About 15 years ago I had them in a dwarf seahorse tank, I panicked and tore the tank down because I was told they were bad news. Now that you mention it, I never had any problems with them I was just fearful that I would lol

I stopped feeding the gorgs and have never used phyto in this tank. They're not NPS so I think they'll be ok temporarily. I have considered removing the gorgs just for feeding but haven't done so yet. The tank is free of diatoms, they came and went but were never really all that bad.

Lionfish Lair · Mar 24, 2017

I bet you're on the tail end of them...

Nooonan said:
About 15 years ago I had them in a dwarf seahorse tank, I panicked and tore the tank down because I was told they were bad news. Now that you mention it, I never had any problems with them I was just fearful that I would lol

One thing, I guess, is that the way we fed our dwarfs and fry the numbers could easily get out of hand and it's next to impossible to break the cycle. There's almost nothing to limit their population growth. I've been reading back to 2001 and I'm not finding anyone saying they actually stung their fry/dwarfs.

Nooonan · Mar 24, 2017

Lionfish Lair said:
I bet you're on the tail end of them...

One thing, I guess, is that the way we fed our dwarfs and fry the numbers could easily get out of hand and it's next to impossible to break the cycle. There's almost nothing to limit their population growth. I've been reading back to 2001 and I'm not finding anyone saying they actually stung their fry/dwarfs.

I hope so! I'll give it some more time as I try to manually remove them for now but hoping they all start to die off soon. Thanks for your expertise!