Let me guess...

[Lucid]

Is this Aiptasia sp.? I have seen them in a LFS and on a frag I got for my Dad's nano. But this one looks somewhat different. It is about 3/8" across the head and the face of it is green. In the actinics it glows like other corals. I noticed it almost 2 weeks ago and I have been observing it to see if it is growing etc. Yesterday it was one, and today I noticed it had split into 2 smaller ones. :/ I got my kalk out, ready to make some paste, I just need to know for sure.

Pics are bad, it is in a location back of the tank and I could only shoot at a 45 degree angle to the glass. I cleaned it up best as possible in photoshop.

[Doodaa]

looks more like a zoanthid to me, but I am no expert.

[TimH07]

its in no way aiptaisa, its green, aip's are clear/brown, that looks kinda like a palythoa of some sort. my guess

[Lucid]

that is what I was wondering. though the tentacles have some up and some straight out like aiptasia (from what I can recall). if it is a zoa, it is a hitchhiker.

[Lucid]

update: the newly split one has been moving further away from the parent one. like about 3" apart now, with no connective tissue. can zoas/palythoas move around like this?? it does look like it has a foot like other anemones.

[DarthClownfish]

I don't believe that zoas can move. Sounds like an anemone to me

[Lucid]

If it didn't have the green face I'd say it was definitely was aiptasia. Like TimH07 said, I am used to seeing the clear brownish ones in the LFS. Would be nice to have an aiptasia expert shed some advice before I kill them with kalk paste... just to be positive.

[metalhead]

Hard to tell with those pics, kinda blurry.

The tentacles definately look anemone-ish though I've never encountered a green aiptasia before. I have and have had plenty and all of mine were clear to brownish in color.

Can the rock they are attached to be easily removed? If so you may try to quarantine the rock until you get a positive ID. This will also make it easier to treat them if/when the time comes and keep them from spreading throughout your main tank in the meantime.

All that said, if it were me, judging by the rate they seem to be multiplying and if I had no other options I would kalk their butts off!

[Nemo Keeper]

If Aiptasia is white/brown, I have that growing in my tank. Is this something I need to get rid of? If so, why and how?

[TimH07]

If Aiptasia is white/brown, I have that growing in my tank. Is this something I need to get rid of? If so, why and how?

it can spread incredibly fast and stings corals, i tried burning them with boiling water at the stems and the remaining tissue became 5-8 new ones, and each one of those made 4 new ones, in a few months i had too many to count.

i got lucky and the 3 peppermint shrimp i bought actually ate every one of them, including the large ones (size of quarters) that most reefers agree pep.mint. shrimp wont eat. really lucky.

edit, i'd like to retract my "in no way" statement, i should say that i've never seen green aiptasia but im betting anything is possible, i googled some images and that shape is characteristic of normal aiptaisa, but i still cant find a green one. is it truely green or reflecting colors around it a bit?

[Nemo Keeper]

So how can I kill them?

[TimH07]

there is a new product out called aiptasia x

youtube has a video of it in action, it seems to work rather well, there was a thread ninong posted with information not long ago. if i had them still, i'd try it.

[Nemo Keeper]

OK, just saw a few videos on the stuff...looks to wrok REALLY good. However, do you know if the residue that's left behind is dangerous for other living polyps or anenomes?

[TimH07]

it kills them, so i'd imagine it is, the idea is to make sure you use just enough for it to work.

[Lucid]

The weird thing is they aren't getting big, yet. That has puzzled me, the only thing the first one did was split and hasn't grown in size.

metalhead- the rock they are living on is a big one and in the back. I can just get to them with my finger. And I have 4 others piled on that. I guess I am somewhat lucky they are out in an open spot so I can nuke 'em.

TimH07- I figured they were aiptasia, but maybe a different species not so common. They glow green under actinics and also look greenish, but translucent in the daylight lamps. Got me stumped.

Nemo Keeper- I had one on a coral frag in my Dad's nano. I used kalk paste and a pipette to deliver death. Worked really well, but I have heard it may not get it all and more will grow from the bits left over. I used a good heaping helping and it worked. Though, be careful with any nearby corals etc. I will burn/kill them too. I took out the frag in a bowl + tank water and did the deed. To make kalk paste, use kalk (pickling lime) and a couple drops of water. Mix to a toothpaste consistency.

[TimH07]

a pretty nice anemone site just for looking at kinda off topic

Google Image Result for http://actiniaria.com/img/aiptasia_couchii_1.jpg

[Future]

Look up "Majano Anemone" see if it looks the same. They tend to have a greenish tinting.