I have a disease chart with one of my medications by Mardel labs. I think you probably have one of two things going on: flexibacter columnaris or a fungal infection.The chart on my antibiotic describes "greyish white stringy material covering most or part of the body: white or grey patches" as Columnaris (not a true fungus, but an actual bacterial infection...this is what I am treating on the mouth of my Lemon Tetra). The lesion on my fish is pure white and flat, isolated to the upper lip.The other description on the Mardel chart is for true fungus, which is "whitish tufts of cotton like material found on the fin tail and body at sites of injury." This is a true fungus, not bacteria.
My other suggestion is to bring your pics to the LFS and see what they say. It's hard to know what to do, as you will get 10 different suggestions for what to treat these with. According to the Mardel Lab packaging, Maracyn treats both. That is what I am using for my fish. My fish are still alive & the lesion has not spread, but it hasn't gotten smaller, either. Either my dx is off, or I need to change to another med here soon.
I would do another water change, too, since water quality is so important. I assume your chemistries are all okay. I really regret not having changed my water more when I was starting to cycle 2 mos ago. I think it was the fact that I "let me tank go" for five weeks that brought on the stress & disease in my fish.Oh well, lesson learned.
About your fish- Flexibacter Columnaris (the bacterial infection) is a bacterium present in the tank as a normal flora, and it is opportunistic. So, perhaps the stress of moving to a new tank stressed the fish & brought it on? If you have a case of true body fungus- I would think that an injury would have had to occur. Are some fish attacking the others? I would be leaning toward flex, but I'm just a novice. Maybe someone with experience will post their thoughts. Again, the folks at the LFS might be a good resource. Good luck!
Ps- You may already know this, but if you end up treating the entire tank with medication, you'll need to remove the carbon filter. Alternatively, you can remove the affected fish to a "hospital tank" to treat.
