From personal experience, I have gotten cuttings (clones) from friends without either parties knowledge of powdery mildew. Some strains are more receptive to the fungi then others. That being said it can thrive in the right environments laying dormant. Beware of any leaves that look like this ^
Spores become airborne when disturbed so be careful not to allow them in the Bloom environment.
An organic remedy is a sulfur foliar spray which coats the leaves and effects the ph making it inhabitable for the fungi to live.
If you have a clean clone, the BLOOM will provide the perfect temperature, humidity and air flow to deter spore colonization.