I keep one ball python (for almost 15 years) the traditional basic way -- coco chip substrate, some cork and plastic hides, a water bowl. I've not had mold in his enclosure (PVC with an RHP) once during that time. Simple cleaning (not even that frequently) is all that is necessary to avoid it.

I keep about 15 "bioactive" vivs for frogs. Most of them have some fungus much of the time; one grows a crop of mushrooms reliably every two weeks or so (they're neat). Fungus is an inherent part of bioactivity (if all the fungus on earth were to die, there would be no bioactivity at all; we'd all die too within a couple years from starvation).

The best protection against fungus in my experience is to moderate moisture levels (easy in a ball python enclosure, since the substrate can be basically dry so long as there is evaporating water to keep humidity at a decent level, and a moist hide box for the snake to go during shedding). Some substrates mold for no reason at all (Eco Earth style coco fiber does this bad), so swapping substrates might be a solution. Sounds like perhaps you're adding too much water in order to make up for shortcomings in enclosure design (just something to consider -- not intended as criticism or accusation).