grow problems

I have a problem and I’m hoping someone can help. I startedover several times because I thought I had the tobacco mosaic virus but my problemkeeps occurring. I used several different strains with new soilless medium andI sterilized everything. I’m starting to think it must be something else thatis causing the problem. The problem isusually noticed in the grow stage near the top of the plant and it starts onthe new growth. The new growth stops growing and it starts turning a light but dullgreenish yellow with contorted as well as thin shaped leaves. The problem movestowards the bigger leaves near the affect new growth and starts turning them apale dull green color. The leaf margins fringe upward while some leaves show afew white lines here and there. The white lines look like lines of stresswithin the leaf. The roots look nice and healthy. I use grow big, big bloom, liquid karma, humic acid 15%, dry maxi-crop and cal-mag. PH: 6.0Climate: 74 degrees 50-60% humidity and pro-mix HP. 600 watt metal halide is 2 feet above top of plants. What could be the problem, what is it that I’m missing?