Help...not sure whats going on with my girl...(pics)

This is my first post and any help would be greatly appreciated! AK-47 clones started in rapid rooter, with a Humidity dome. After 10 days i move them to a aerocloner and the roots have exploded. However, one plant has this weird white fuzzy stuff on the stems and at the base of leaves. New growth distorts and shrivels up after a few days. I've searched the site, internet, and looked in the bible, but cant really seem to find anything that looks like this...

Running 1/4 strength AN mico/grow/bloom with b-52.
Temps avg 72 with lights on, 64 with lights off
RH averages around 35 and 45%
Light cycle 18 on 6 off
PH 5.7 to 6.0
PPM 850

Looks like powdery mildew. Sorry to say it, but you should trash the plants, wipe down the room with 10% bleach solution (or do a sulphur burn) and start over. PM stays in the plant's cells and the white mildew is just it's way of making spores. There's no way to cure the plant and if you decide to keep going it will keep popping up and potentially make your buds dangerous to smoke. Are you seeing it on the leaves too? That's where it usually shows up but can also be seen on stems.

A lot of people recommend Serenade for PM, and while it's a good product its like a condom...preventative not curative

Your humidity levels and temps are where they should be. It might have come in on your plants or when you used the humidity dome (which could have had 90-95% humidity). Your PPMs seem awfully high which would explain the distorted and leaves. How big are the plants? If they're still just seedlings 300-400ppm is where you want to be.

ahh man that sucks! I was really hoping i wouldnt hear the dreaded Powdery mildew words