Did the white clump on the gourami look like a haystack?
I just got through fighting columnaris, and a lot of what you're describing is what we went through.
If it is columnaris, you have a journey.
This article was a good resource for me. @CoralBandit was also a huge help.
Here's what I did:
Lower the heat and add salt. Dose Furan-2 and KanaPlex fully following instructions. Spot treat visible "haystacks" with hydrogen peroxide. Toss the substrate. Bleach the ef out of everything. Immediately euthanize any fish that look sick. Treat the entire tank (both of them) with potassium permanganate. Putting it back together, because I destroyed every single bit of nitrifying bacteria, I got an Angels Plus active filter.
It SUCKED, but we're on the other side now. We're waiting until the 22nd to replace fish (okay we're *mostly* waiting), but the fish who survived are doing well.
If you have any questions, I'm absolutely willing to answer. I read everything I could find on the topic.
It's good to trust your gut about getting rid of whatever is toxic in the tank. You can do it!