Great 600 w light kit. Includes cool-tube reflector, MH and HPS bulbs, Digital Ballast, and hangers. $269.95! free shipping!
http://www.ebay.ca/itm/600-W-MH-HPS-DIMMABLE-DIGITAL-BALLAST-AIRCOOL-TUBE-KIT-/300580591209?pt=LH_DefaultDomain_2&hash=item45fbffd669
the yellowing could be caused by too much nutrients, and this could also be affecting the plants ability to intake water. The yellowing could also be because the plant is receiving less nitrogen now with the bloom nute's. I would be mixing in veg and bloom nutes together at 50/50 for the first...
A plant only has a set maximum production, its not just about amount of lumens. If you overkill on the lights then your just wasting money because the plants can only use up to a certain amount, then their limited by other factors, and by their natural growth rate. you need to learn a lot more...