WeedHound - I don't know if this applies to your particular problem, but you know the pH problems I was having and I've been able to get things under a lot better control since I sterilized everything.

For those of you contemplating coco, be sure to wash your coco really well when you get it. Coco often has a lot of salt in it and there's really no way to know if it's clean except to flush it. One grower here says Canna brand coco is good without flushing, everything else, wash real well.