algae in tank, but please identify this

[reef tank 2.0]

if you read an earlier thread of mine, you learned that I am having a bad break out of algae in my tank.
shortly after I started this tank up (1-1/2 years ago), I started getting algae popping up. it started on the left side of my tank. Occasionally, I would use a soft bristled toothbrush and try to scrub it off, as well as a baster and blow it off. But it always came back. this was the beginning of my algae break out. it is very aggressive and it only resides on the left side. this tank was started with dry rock that I had in my last tank that sat dry for about 4 years.

This "stuff" is purple. recently, it seems to have gotten bigger heads which now makes it look like some type of "star polyp". They hold tight to the rock and do not wave in the current. I have never had these intentionally, so I'm thinking they came in on a coral frags that used to be in the area.

the top layer of rock can be removed and scrubbed completely but I have not done this yet. the base of my rock are glued together, so removing those is impossible without disrupting everything or breaking rock apart. would love to avoid doing that at all cost.

Here's a couple pictures with blues OFF
question is....what is this stuff and how do I get rid of it???

 

[dvgyfresh]

Blue synpodium? Is my guess I’ve heard they are hard to get out once established