Turtle fungus or skin shedding?

i have a painted turtle about a year and a half old that has a white "cotton like" film on him. some days its better than others, i went to the pet store and they told me it was probably a fungus and i should give him a salt bath daily. well after about 3 weeks of giving them to him, the problem still isn't clearing up like i thought it would. with that not going away, i am now thinking that maybe he is shedding his skin. Some days its really really light, some days its really bad. (he has grown twice the size he was from when i originally got him 2 months ago). You can only see this under water, and when he is outside of the tank, he looks perfectly fine.

to get rid of all the people that are going to say that im not taking care of him, or he is sick let me get this out of the way

He is happy
He is eating normally
He is a really fast swimmer, and can run even faster.
He is in a 55 gal aquarium
He has a filter that is adequate for the water
I change the water and clean the gravel completely every week
His UV basking temp is about 95 degrees
He does have a spot to completely dry off
He has a calcium bone floating that he does nibble on
There are also 2 48" florescent lights hanging above the tank to provide light for him all day long.
Lights are on 15 on, 9 off every day

Ok now my question, the internet has failed me with my searches for pictures or good information about turtle fungus' or shedding. so, do any of you have pictures or information of what either of them would look like? The "cotton film" is on his skin, not on his shell. His shell is healthy and hard.