Sorry for your loss. I don't want to pile on, but the lesson to be learned here is water quality. I've seen those weird white patches in Ropefish and catfish. And the common thread with all of them is poor water quality, and diet, usually due to over feeding. Keep in mind that carnivorous fish shouldn't be fed every day. I'm not sure what size tank your fish are in, but IMHO, it sounds a little over crowded as well. It sounds a little too "Community" orientated. The various types of fish you have would do better in species exclusive tanks.