Early Stages of Aiptasia?

looks like majano which are also a pest anemone. I would not introduce that rock into your display tank.

 

+1 also looks like majano to me

 

Hot boiling water try that and keep an eye on it

 

You can use LR in qt, you just cant medicate in it which would defeat the purpose. But bad nems range in various colors and such. I had some that looked almost cool, blue and green stripes. Once saw what I thought was coral that I wanted to buy until I was told they were bad nems. You can use various ways to kill them. I have tried a few with little success. The key seems to be getting them OFF the rock. Ive injected them with a needle and pickling lime, which they really dont like but then you have to scrape them off. If you leave them, they usually come back. Tried some of the commercial products, white chalky substance you are suppose to get in their mouth. Worked but they came back. Also dropped some on a zoa and it closed up for about a month and came back. Ive seen some kind of electrical stick you zap them with. But they are pretty hardy. I had a rock with one on it, sat it in my driveway for a few weeks and it was still alive.

 

lucky it is in the qt tank mate