He started developing white spotsHi Kevin,
Welcome to Reef2Reef!
Your tang is showing a symptom of possible disease - the rapid breathing and laying on its side. It also looks like it’s eyes may be a bit glassy? This all can be a symptom of a very serious gill disease known as velvet, Amyloodinium. I hope not, as to treat it you would need a treatment tank and dose it with copper right away.
The high temperature wasn’t good, but was not high enough to case this serious of symptoms.
Jay