It looks a lot like Hexamita or cotton wool disease... These are common with Angelfish.
Is the fish still taking food or is their behavior strange?
If still eating you can get medicated food... If it's not you might need to either QT it, or dose the whole tank which might be best as the
parasite that causes hexamita is still in tank. It's not too late from the looks of it, but the clock is ticking.
When in doubt I use the med trio that Cory from AQ CO-OP is always recommending. It works just have to follow instructions to the letter.
I hope the poor dude gets better
Is the fish still taking food or is their behavior strange?
If still eating you can get medicated food... If it's not you might need to either QT it, or dose the whole tank which might be best as the
parasite that causes hexamita is still in tank. It's not too late from the looks of it, but the clock is ticking.
When in doubt I use the med trio that Cory from AQ CO-OP is always recommending. It works just have to follow instructions to the letter.
I hope the poor dude gets better