Just to add, i would of taken the same actions myself (and have done in the past), somtimes its just too clear when a fish has past the point of comfortable return.
completely agree with this, sometimes you just know it's gone too far for the fish to ever recover.
just to add one of my experiences with angels that I think supports your decision, I had a lovely black angel, had him since he was a baby, shortly after getting him while I was stocking up a new tank one of the fish I got was carrying some disease but showing no signs of it, within a week or so of putting him into my tank half the fish were dead, tried everything i could to treat them but nothing works... sometimes it just goes like that. That disease killed every fish in the tank except for this one angel, lord knows how he survived but he managed to fight it off. he was always weak from that point onwards though.
Then a year or two later Ian decided to set up an angel tank, so we moved him from the community tank he was living in to Ian's tank. The tank's pretty tall and he decided he didn't wanna go in, just as we were about to put him in the tank (so bear in mind he was currently about 6 foot above the floor) he flapped out of the net and fell to the floor. We thought that'd probably have killed him but stuck him back in the tank to give him a chance, and he recovered, from that point on he was even weaker than before, never a strong swimmer but no you'd see him struggling just a bit in the flow of the filter if it had just been cleaned out.
Maybe 6 months after that Ian set the tank up as high tech planted, set up Co2 on the tank, all was running fine, then overnight one of the cats must have kncked the regulator. We came down in the morning to find the fish all floating aimlessly around the tank and Co2 bubbling away. Most of the fish looked dead or at least half dead but we switched the Co2 off, put an airstone on and left them for the day to see what happened, when we got home we found a few casualties but quite a few had recovered, including this one black angel. However he was clearly not fine, obviously from being gassed he'd suffered some sort of respiratory problem and couldn't get enough oxygen.
Within a week we had an outbreak of whitespot in the tank (not surprising given the trauma) cured it with no losses but the poor black angel was looking decidedly ropey by this time.
This was about a year ago, since then he's always had problems swimming and is fairly often found gasping a bit. I thought about putting him out of his misery a few times but always decided to just give him one last shot. He passed on last week sadly. Looking back at his life and how poorly he was I think it may have been better to euthanaise him (hindsight is a wonderful thing), so always giving the fish one last chance, may not be the best thing to do in the logn run.
just thought i'd share that anyway.
regarding the current situation, I would definately give the tank a dose of strong antibacterial med just to be on the safe side.