CBB w/ grey spot on gills[Large Pic]

Picked up this CBB about 1.5 weeks ago from a local reefer who had stuck him in a 20 gallon sump compartment after he developed a taste for expensive acans.

Destroyed all feather dusters in tank within a couple days(had a fair bit of em). Eating as much scallop elastic banded to a rock as I'll give him(soaked in brightwell angel elixir). Also eats mysis/brine but not as much enthusiasm.

Acclimated with a drip line to bag in sump over 45min.

Tank is a 120g containing SPS/LPS and 2 Osc.clowns, midas blenny, possum wrasse, DWG, and potters angel. Smaller clown(under 2 inches) nips at him when the feeding rock gets put into the tank but the CBB doesn't seem to really care. Puffs up spines sometimes, but otherwise ignores the clown and just keeps eating.





Woke up this morning and noticed he had a patch of grey scales on his left side. No signs of distress or changes in behavior. Eating fine etc. Any ideas what this could be?





Link to pictures(wont let me post here):imgur.com/a/wQRTv



Tank: 120g

Sump:50g

Nitrate: 0-5ppm

Nitrite: 0ppm

Ammonia:0

PH:8.2-8.4

(all using API test kits)

Salinity 1.025

Temp: 79.3