why does fungus love my oncs?

[Optimist]

Maybe some more air movement through the roots, and a fan to send more air around the plants. Many people forget that air movement is a requirement. You can get small clip on fans, some solar, at a lot of places. Air movement through the roots will cause less "muggyness" which might help with the fungus.

A thing to remember (maybe) is that fungus spores are in the air. If you have an indoor grow situation, possibly you can put some kind of filter over your heat ducts or air vents and then do a thorough clean of your indoor space. It would not be strange to consider that the spoors may not be of your doing. They could be coming from a moldy basement down the street or any other situation.