I have a yellow lab that has a red area at the base of both pectoral fins just behind the gills. The red area also moves when the fins move so it must be partly on the fins. Water parameters are: Nitrite: 0 Ammonia: 0 Nitrate: 10-20, pH:8.3, GH: ~300ppm. I recently added API stress coat in the tank due to a fight between two cobalts that resulted in missing scales and also added 3T salt per a gallon water Saturday to help generate slime coat. What could this be and what should I do about it? Thank you!