I very rarely see any of the Gouramis picking on another one. The Opaline will mainly chase the others around from time to time, but to actually nip at their fins, I haven't see it. The Barbs mainly stick together. Every now and then they'll split up and one will chase another fish, but I've never seen this go on long enough or frequent enough to think that's what's going on.
Yes, I did add a Ropefish to my tank without QTing him (I know... I know) and I believe he did come home with some parasites. I posted some pics of him a while back and someone said it looked like Anchor Worms. He must've brought Ich with him as well. Since then I've been treating the entire tank using the heat method (no salt) and I dosed the tank with Jungle Ich Parasite Clear.
While all of this was gong on, my male Pearl Gourami developed some redness on his dorsal fin and it began to look kind of ragged. He also stopped eating and just hovered under the waterflow from the filter. I tested the water and the nitrates had risen to 40-80ppm. I immediately did some PWC to get it down to about 20ppm and started dosing with Melafix. He's doing 100% better now and I thought I was going in the right direction until I noticed that one of my Dojos had lost his dorasl fin! I decided to try to treat with Jungle Fungus Clear to see if that helps and so far it seems to be.