Safer® Hydro FAQ: Why is there Fungi in My Grow Room?
The ideal conditions for mold, mildew and other destructive fungi are heat, humidity and available nutrients such as nitrogen – exactly what you have in an indoor garden.
The spores (like seeds for fungi) can get into your grow room from soil mix, your clothing, or even the air. Once they find a warm, damp spot, they begin to reproduce, showing up as slimy, black, gray or whitish spots in nooks and crannies where they're shielded from light that can dry them up. Fungi are not only ugly, they can spoil your crop, gum up your system, and entice pesky fungus gnats into your garden.
Prevent fungi from moving in by taking care to clean up spills and splatters of nutrient solution, which they feed on, and by eliminating standing water everywhere in your grow room. If you do see fungus forming, use a safe, but effective sulfur-based fungicide to wipe it out before it can do any damage.