Hey all, just want to chime in.
Okay, it's not velvet, velvet looks much different and you'd be able to see it with your own eyes as well. What looks like is happening is body slime is being generated too quickly because of the AQ salt and it's start to shed, making a slimey appearance. It's also effecting the eye's, AQ salt makes pop-eye worse because it retains fluids instead of expelling them like Epsom salt does.
What needs to happen is just a full water change to get rid of anything, I didn't see what size tank he's in right now but Lena, if you can do a 50% change one hour and an hour later do another 50% change, this will help reduce his stress. Give him the rest of this day off from everything.
Make his tank at 80 at the most, pop-eye doesn't need any special heat requirements and best not to stress him out more with different water temps.
Since we don't know whether this is gram negative or gram positive, it would be best to do a combination of Maracyn I & II so to covers everything. That will basically cover everything that KanaPlex would cover but the difference being that one medication is less stressful than combining two medictions is all. But that's neither here nor there.
So what you can do Lena is start the Maracyn II treatment and combine it with the Epsom Salt at half dose (.5 tsp/gal) while you try to find Maracyn I (not Plus or anything like that) and then if the Maracyn II doesn't work, switch to Maracyn I and no ES.