well when i rescued him from the petstore he already had it..he was in really really dirty water and in a really tiny cup with decorations in it giving him little to no movement whatsoever.
i brought him home, gave him a salt bath, and put him in a gallon vase cuz i didnt have the 10 gallon set up for him ready. i bought him JFC to clear his fin rot and hopefully get rid of the white i saw. after 2 weeks or after the second dosage of JFC i moved him into a divided 10 gallon tank..the whiteness had seem to start fading away. also the other fish i rescued in the same conditions as he was made a full recovery. After a couple of days i noticed the white coming back and now it looks more noticeable..it hasnt grown or spread but just got a darker white.