I keep my Angels at 80 - 82 degrees. They can withstand very high temps and I keep them in the garage where the temps goes up into the 90s during the day.
It's hard to tell whether it is a Koi Angel. Koi Angels have see through gill plates that makes them look like they are blushing when young. It gets covered though with irridescent pigments when they get big. Another charateristic Of Koi angels which they continue to express in adulthood is that there are no straitions on their fins. Hard to tell with your fish though due to the dark pigmentation on its fins. Typically kois do not have the amount of marbling on the their bodies as your fish.