You might be over watering. Let the media dry out more between each watering. Otherwise, Is it very humid in the grow room? Air circulation?
A little bit of white fuzz (or even some green, or yellow) isn't typically a big deal; you might just stand for some better air flow. Use an oscillating fan.
Usually these are strictly saprophytic fungi, breaking organic matter down. Some are opportunistic and might attack a weak plant. For example, if you were over watering it would create an anaerobic environment, which if prolonged would cause the roots to suffer and potentially succumb to such an opportunist (these are ubiquitous). All soil has some fungi in it and threads of mycelium which usually you just can't see.