As I was putting my new toadstool into the tank I noticed a clear dime sized creature with 8 legs swimming exactly like an octopus... Is there anything else this could possibly be? I tried getting a picture but it would not show up. It was really cool looking and I couldn't discard him... Hopefully it wasnt a huge mistake putting him in the tank.Thanks
Generally, no. But before you get your heart rate up, they can and often do die off on their own. However, if you still notice them hanging around in a week or so, then you could probably start being on the defensive. If they ever get up to colony size they can be a pain in the butt, and they pack one heck of a sting. They can, if they get large enough and are of the right strain, eat certain smaller shrimp.
They do require the typical things required of a nuisance pest, very similar to aiptasia actually, namely they need excess nutrients and something to feed on, so you can starve them out in a similar manner. There are livestock options that will eat them, but until you have a full on infestation I would advise against that. Not only are the options not very suitable for most reef tanks, but even the right nudibranch would end up just starving after it took care of them.
Also, the old standby of kalk paste is reported to work well.
Was it slightly tan or brown in color? If so I have seen an apistasia ( I always spell that wrong) in a swiming mode the exact way you are descirbing. Cephlapods usually dont swim like that they use "jet propulsion". I saw what you are describing when I brought a new coral home and got it on video. ( I must have deleted it) But anyway I posted it here and was told apistasia buy multiple people. It was freaky watching this thing especially after I knew what it was. It hit the wall of the container and climbed up the wall like a spider. Gross!
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