I get minor flakes of the ASTs skin on the sponge prefilter. But not noticeable flakes of skin and shell. I've only seen major peel on turtles kept in less than clean conditions or malnourished. Looking at the feed list, I'd say the turtle was getting enough variety in its diet. Although, I'd switch the krill for raw market shrimp or live crayfish due to the amount of oils in krill. Oil on the water surface reduces the water's ability to exchange O2, CO2, ammonia, etc.
I'd also stop serving feeder goldfish and use bait minnows if live food is desired. The copper levels used in feeder farms will eventually damage the livers of aquatic turtles. Live foods can be gut-loaded with plant material, turtle vitamin supplements, etc if kept in a bucket or bin for a couple of hours before offering them to the turtle. The better the food; the healthier the turtle.
After a snapper is past 6 months old, it's also a good idea to provide 'fasting' days of once a week until it reaches a year old. Then, skip feedings every third day to allow the turtle to purge a bit to prevent obesity. If a snapper's tail looks full and round, it's getting enough to eat. I've seen snappers that can barely bend their legs from being too fat.