are you sure he told you to put iodine? or did he tell you to put salt? If he said salt, he was referring to sodium chloride, not table salt. Iodine is not good for living fish. It's mainly used for salt water inverts and corals. And if he did in fact suggest iodine, he should have told you to dip it, not add it to your actual tank. Try taking better photos, dark room with aquarium light. Is the rot getting worse?
Okay, I just read your other post, sorry didn't see it there. Iodine, can be toxic to fish, if you wanted to clean and help create antibodies, you should have used a antibiotic like fish mox to prevent infection, or bacteria growth. What "Iodine" did you use? On the bright side, your fish looks healthy. His fin will grow back like the other guy stated. My first guess when i responded to your post was anchor worm, but it did look like ray damage. My fish didn't have the red like yours though, it was more of a skin bump.