Getting stem root where the lower stem weaken's and gets smaller. Using rock wool and sometimes its turning green when it starts yellow. This happens in veg only under a 200W CFL and when the seed is about 3 weeks old. Things I'm doing: -Its not from water level being too high. -Could be from covering up the net cup w/reflective mylar? I could a hole as big as a quarter so the seed can grow up through it. I do this so light doesn't leak through net cup and get into my rez. -Only putting 1-2 layers of stones in the bottom of net cup.. Whats doing this??