Hi, Pictures 2,3, & 4 I can definitely tell you it is Aiptasia. Generally this is thought of as a very pesky creature because it grows and spreads quickly sometimes out of control. It stings fish and other sps/corals that it comes in contact with. It is very difficult to get rid of once it's out of control, most people get a special solution you can buy that you have to inject into them I believe which is mostly made of lemon juice and some other stuff. Some believe that a gold banded butterfly fish is a natural controller of Aiptasia. (I think that's the right butterfly fish, if you google aiptasia you'll be able to get some great facts) I personally have gotten rocks out of the ocean and and had aiptasia in my tank before and thought it was pretty cool. It only spread to become about 3 of them total. I would feed it and like to watch the tentacles pull the food in. I would just keep an eye on how much it spreads, it looks like you have quite a bit already! Good luck with your decision.