Please need help diagnosing my Coral beauty

[PdThaDude]

Okay let's get down to the basics first tank salinity 1.025 ammonia 0 nitrite 0 nitrate 8ppm tank temp 77 degrees Fahrenheit 60 gal with sump running a dual Reactor with gfo and active carbon. Tank has been running for 4 months. Stocking list two clowns two pajama Cardinals one rainbow bubble tip and some polys. Feeding frozen mysis shrimp and some garlic fish flake
No I did not quarantine him I feel that this fish store was very trusted so please spare me the lecture, and I will be quarantine and everything from here on out
Okay on Thursday I received a coral beauty as a gift he was given to me because I've been talking about him and watching it at the local fish store for about a week he had great color when I got him I was told he was very hard to catch and the tank at the store. I drip acclimated him for 2 hours. The first two days everything was going fine he was adjusting nicely and eating like a pig. I did notice on his second day in my tank he was having a really big green stringy poops. But I felt that he was eating off the algae sheet at the fish store. On Saturday I noticed a small white spot on his right back half so I went back to my fish store to buy some water to do my two weekly water change told the guy what was going on gave me some melafix. It is now 24 hours of dosing the medicine with carbon turned off and skimmer turned off the white spot is getting bigger and now is on the other side as well and tonight he decided to go on a hunger strike. The pictures I will touch the first two are on Saturday the second two were taken on Sunday thank you for anyone's help and advice would really not like to lose him
I'm sorry for my bad grammar I was trying to get this post out quick

[PdThaDude]

Disregard the first picture this one was supposed to be in its place

[Swensos]

By "white spot" do you mean pale area on its sides? Are its scales missing from those areas?

Has it been rubbing itself against anything?

I don't know if melafix will do much. If the pale areas are showing red/bloody, it could be uronema. Or it could be a skin parasite. But you also said it's not eating...