Help Identifying And Treating An Ongoing Problem

[andyw823]

The problem first started approx 4 months ago which affected Rainbow 1. It started as a small white blob on the upper lip which soon spread around all the mouth area. I started treating with Interpet anti fungus and mouth rot. At the same time I noticed another Rainbow develop the same small white blob (rainbow 2) I ran the course of treatment which had zero affect and both fish got worst. I then did a 40-50% water change and switched to Waterlife Myaxin again this had zero affect, I also tried Pimafix this had no affect either. I gave up with the meds and left the fish alone, rainbow 1 got better after a month while rainbow 2 had made a 90% recovery. But then rainbow 1 got bad again and still is. A 3rd rainbow is now affected and in a bad way, overnight it seemed to develop the same white growth on its mouth, a few days later it's mouth has fallen apparat. Before I start treating I need to know what the problem is and what the right course of action is. I've included 3 pics.

Rainbow 1

Rainbow 2

Rainbow 3

 

[N0body Of The Goat]

Rainbows are reknowned for needing weekly big water changes of at least 50% to keep the water quality excellent and prevent columnaris. This most recent case almost sounds like mouth rot, but fish illness and treatment is not something I would bet my own life on.