hey jason, im no "Expert" so i cant tell you what exactly is going on with your acan. has your acan been showing its feeding tentacles at night/do you have any critters that nay be bothering it? my suggestions would be to give it an iodine dip in case it is a bacterial issue that may stop any further tissue loss then move it to an area with less light. try to spot feed it directly if it shows a feeding response (easiest at night) also what are your ammonia/nitrite/ate levels at?
It doesn't look like if it is melting but it looks a bit retracted. Your parameters sound good except specific gravity. It is too High. I keep mine at 1.025. Try reducing this and placing it on one spot with less flow and light for some time.