If the leaves are turning yellow around the edges and curling then it could be that the hps is a little too close. To get the right distance move the light so that you can hold your hand at the top of the plant for a minute before it gets too hot. Then move it up another 2 inches from that distance and you should be set. Just continue to keep the light that total distance away from the plant as it grows.
hatecable Reviewed by hatecable on . Leaves become yellow under hps ?! Hey mates I was growing under 150w cfl and soon I switvched to 400 hps but still 18/6. The last two pairs of leaves on my plant are a little yellowish and more thin than the previous. The lamp is 35cm or one foot far from the plants... Also is there a chance the preflowers to look like male the first few days and than to produce pistils?? Rating: 5