It is like a white, papery sheet that grows on him overnight, and it flakes right off and sinks when I get him to swim around. It covers his sides, and doesn't really grow on his fins. It has grown on him overnight for the third night in the last week, and the three days were not consecutive. These pictures show it after most of it has flaked off this morning.
I think he might also have some fin rot issue on his tail fin, though it doesn't seem to get any worse or go away, so I'm not sure if this dark streak is just his natural color or something. It looks a little raggedy on the end, and it wasn't like that when I bought him:
I bought this betta about a week and a half ago, and he seemed perfectly healthy. The night I brought him home, he sprouted some cottonmouth fungus, and I began treating him with jungle fungus eliminator and stress coat in a half gallon tank with daily water changes. The cotton fungus stuff seemed to have cleared up, and he seems to not be suffering. He eats eagerly, swims around when he sees me, and the fish was blowing new bubble nests every night up until last night. He did not make a bubble nest last night, which has me worried that he may not be feeling well now.
I have been thinking about returning him to the store, because I do not know how to treat this and maybe they could treat him at the store...