Please don't take this the wrong way, but if you ask for answers/opinions, you're going to get them on this board and people won't hold back. I have read just about all of your threads, and you are constantly having issues do to not following accepted techniques for properly keeping a saltwater aquarium.
Honestly, the stock list you have going on in this tank, the bioload it produces and the fact that you only do water changes once a month is all harming your fish.
Your stock list is stressing your fish out. You're not quarantining, so you may have introduced a parasite to your tank making things even worse. If you say something white on your fish and now it's gone, that to me sounds like Ich.
You really need to get rid of that eel, I am 90% sure that it's stressing out your fish. To add to that, you don't have that much live rock for the fish to hide from one another when they do get stressed.
As for the bladder issue, it's probably an internal parasite, as you did not quarantine this fish to rule that out. What does it eat?
I saw in another thread that you're now thinking of keeping a Rhinopias. IMO, you have a lot to work on before you try one of these harder to keep species. They need pristine water parameters and take some time to get to eat. If you're in the practice of only changing water once a month and using tap water, I guarantee you that this will cause major issues with this fish.