What is this? A tube anemone?!?!

It's a glass anemone or commonly known as aptasia. It is a pest kill it asap, and kill it well, as they will spread and they will sting anything it's near.   It you have kalkwasser, make up a paste of it, turn off your powerheads and paint it on the anemone or use a syringe and squirt it on.
http://www.reefcorner.com/SpecimenSheets/aipatasia.htm

 

Get rid of that stuff asap because it spreds fast! I good way to get rid of aptasia is peppermint shrimp. I had about 20 or so aptasia's in my tank and got sick of it so I just put 2 pep shrimp in there and within 2 weeks they were all gone. Haven't seen one since I have put them in there! Worked great, plus they are kinda a cool shrimp!Hope this helps!

 

Yes, kill it now and kill it carefully by covering it with Kalk paste (or you Aiptasia-X).

I know that they look neat at first, but that one will turn into 2, then 4, then 8, then 16... You get the picture.

It's worth noting that the worst think you can do is try and cut it out or pull it out with your hands. All that will happen is that it will release it's larva and you will have baby aiptasia everywhere. This is one of the reasons that I recommend Aiptasia-X. It kills them in a way that prevents them from spreading.

-JB

 

That Aiptasia-X makes me giggle everytime I watch the video. Great stuff.

 

Joes Juice works really well too

 

I'd save your money on both accounts and hit the local grocery store and pick up a can of mrs wages pickleing lime....it's kalk in a can.....2 bucks and you'll solve your issue

 

My fish have been eatting bits and peices for years and they seem ok.....well except the one that stares at himself in the glass...glad that you got it taken care of. J