Green Star Polyps Issue

[Vincent73]

My green star polyps have been thriving for years, easy and simple to care for. Constantly growing and trying to over take other rocks around it. Now its been several months growth has almost slowed to a crawl and polyps seem to be getting smaller. Tank parameters fine and other corals doing great. The first thing that I noticed when polpys retracted for the night was a very light brownish algea on it and seems if the polyp skin is getting thinner on it. Rock starting to be exposed a bit. I've given it multiple baths in coral rx with a light brushing to remove unknown brownish algea. Normally when healthy skin is nice and purple with long polyps extensions. I could toss them but like the challenge to fix the issue at hand. Any ideas? Pictures with my phone to show are horrible.

 

[Tahoe61]

What lighting type are you using? any bulb changes if it's not LED?
Have you done the basic chemistry? Is the tank running hot?
If flow impeded by dirty power heads, coral growth?

 

[Vincent73]

Kessil A360w, chemistry all fine mag 1350 cal 425 alk 145 ppm and tank temp steady at 78. Mp 10 for flow. All other corals doing fine.