i had one of the small 5'x3'x2' tubs with filter box on top yrs ago... It also had the same lighter blue patches ur seeing o.p.... I never had any ill effects come from it and i dont think its actually chipping. Its almost like the pigment wasent mixed right in the top coat or something. Honestly i wouldnt worry much, but i def understand ur headache/concern. Imo a ray could also drag its teeth down a side wall while swimming, esp a black ray with larger teeth. Anxious to see what they do for ya... Id prob just let it ride myself.