It was gone by the next day.

I just noticed one of my petricola has these big white spots behind his gills. Identical on both sides. Seems healthy otherwise. Still eating a lot, very active, nothing out of the ordinary that I can tell. Water parameters are all spot on. PH 8.2 GH 10 KH 11 0 Ammonia 0 Nitrite About 10 ppm Nitrate...