Weird white thing flaking from dorsal fin?

[Celestials]

Hello everyone! I've been keeping fish for years but am still pretty new to Discus. Of my 4 discus, the deep burgundy one is exhibiting something strange. I noticed it yesterday looking like a white irritation/scrape on his left side near the dorsal fin, and now today it looks like it's peeling.

I'm not sure what this is. Despite being the second largest, he is the most picked on by the others, making me wonder if it's an injury to the scales or something else. He still eats and begs for food and doesn't act ill. His right side looks fine and its usual healthy color, but his left side slightly darker with the weird white thing.

Only other tank mates are a couple little Siamese algae eaters, and 4 baby, quarter-sized Koi Angelfish who are only staying temporarily. The other species ignore him, but he does get pecked at a lot by the alpha Discus. Despite his calm demeanor, he really is a scapegoat. Even the two silver dollar sized young Discus push him around.

In about a week, all 4 Discus are being upgraded to a 100 gal tank, almost twice the size of what they have now. Here are some photos of his 'normal' side and his afflicted side. Sorry for the blurry photos, every time I got close for a picture, he would approach me, hoping for food.21117

[Hollowman]

Looks like you probably added the discus to a tank without any consideration for quarantine. This is 90% the problem. Second, adding fish to an aquarium that have non compatible fish is another problem, fast fish with discus is not good. Thirdly, the fish, even if the biggest is badly stunted and probably has some genetic issue making it less strong and prone to infection. Immediate water changes are needed to clear out the bio load in the water and monitor.

[Celestials]

Actually, I do quarantine my Discus fish. I also preventively 'dip them' before adding them to my home tank to clear any kind of parasite just in case ( as my first two discus I ever bought came from the dealer already infected with internal parasites and another keeper suggest I do this ) Also, my local LFS keep Siamese Algae Eaters in their planted Discus tanks and recommended them to me as the safest algae eager to keep with Discus as opposed to larger growing ones that may even eat their slime coats as they sleep. I do 2-3 water changes a week and try to match my PH and temp each time.

The 3 other discus are healthy and showing bright colors. It's only this one that seems to have a mystery 'thing' that flaked off of him, hence my inquiring what it might be ( i.e. Parasite, ich, velvet etc. ) .

[Celestials]

But thanks, I'll continue with water changes for now. I put him in an isolation tank for a few days and he perked up a lot and his cost is actually starting to look good and much brighter.

[sayid]

i think you are on the right track ,staying in hospital tank for a week or two is good for getting his confidence back ,i would also add a table spoon of rock salt for every 40 liter of water and that would also help his scrape if it is some kind of injury,just keep the water changes so you don't get some secondary infection otherwise he will be fine soon .
p.s the little Buda statue , just make sure it does not affect your ph. good lock