ThanksThat sounds like extra slime coat being produced due to stress. That stress could be from fights or an infection which could also explain the fins or even an irritant in the water.
If you see this on any other fish i would suggest doing a 50% water change and adding 0.25g per L. Or treating with melafix.
Hope I've helped a little, sorry again for your loss.
All over fish are fine, did two large water changes over the weekend as had a revamp and needed to clean gravel where hardscape had been. Was treating with melafix when this happened due to one of my angels looking ragged due to fighting. The aggresive angel has been moved on.