That looks like a sweet colored mojano nem to me! Would be a great addition for anyone w/ a fowlr tank. I could be wrong, but...
I agree...
I've had these before. Make sure that's exactly what they are before you take any action. As stated above, those look like Mojano Anemones, but I could be wrong...
If those are Mojano's... kill them fast before they multiply. I know they do not look bad now, but years down the line you will regret not ridding your tank of these, while you had the chance.
Go to RC, and do a search. There are very experienced reefers who had to break down 200 and 300 gallon tanks because these became such pests. They can ruin any tank and make your LR worthless.
What is the best method of getting rid of these? 1 rock wont be hard as I can remove the rock from the tank. I also have them on another rock that has some zoas on it though