Help, Something odd with my Acan

[GibsonGuitars]

Hello, I have had this frag about 4- 6 weeks and it has been growing quickly... today I noticed some weird browning/discoloration and what looks like deterioration. Please advice if this is something to be concerned about/possible causes or solutions, or if this is something normal a beginner just hasn’t seen before

 

[GibsonGuitars]

S.G 1.024
Temp 79
PH 8.1
Ammonia 0.0
Nitrite 0.0
Nitrate 4ppm and coming down, nitrate was high (40ppm) due to a defective API test kit. Switched to Red Sea test kit, did two 35% water changes over 4 days, started dosing Red Sea Phosphate and Nitrate reducer (1ml) a day yesterday. Second dose applied this evening when I noticed this.

 

[Reefapprentice]

Somewhat blurry in the pictures, but indeed looks like moderate tissue damage on one of the polyps rim to the mouth. Any change of being able to get a better picture? Are you able to see the septa within that polyp exposed?

 

[GibsonGuitars]

Sorry, I got sidetracked with getting laid off from my job. On Monday night late I ended up moving him to be able to get a better pic, and also he was getting a lot of sand on him when the sea hare goes by... and it seems it really likes the new spot. I think it was just the location? If that is possible. It’s been much more swelled up and full looking since the location change (higher up on top of a rock instead of on the sand bed) He is almost healed up, and where the issue was, the is now a tiny new head. I’ll snap a pic tomorrow but I think it is healing up well.