We're a month or so into winter here and I was having a problem with mould growing on the top of my plants too. I had them in a window and the temps were dropping to about 62f at night. The sun never warmed them enough to fully dry the tops of the coco or get the plants growing to a point where they could use the nutes. I cut my water back and had to scrape the top layer off a few times to stop the mould from spreading.
Also my mould problem went away, when i simply increased the air circulation in the grow room.
Edited by Chilidude, 30 November 2013 - 04:22 PM.