Hydroponics Forums Discussions - using a 500w halogen security spotlight

Hey Ron,,nice site:),,this is my first attempt at growing,,im using a 500w halogen security spotlight for my grow light hung from the ceiling of my closet (well ventilated n fanned of course) and using a soil mix,all was going well it seems (they grown a nice bushy 30" tall n 20" wide),,,up until the tips of the leaves of my largest plant started browning and looking half dead,also the deep green in the larger upper leaves seems to be turning to a whitish yellow color between the veins???? i've read that it might be a manganese deficiency but i dont know where to get hold of any or how much to use? (or even if its the amount of water causing the damage) my lil babies r sufferin plz i need help!!!