Droopy leaves, lime color

Hello everyone . I need some help from the pros. These plants are about 3 weeks into their veg ( from cuttings ). Ive never had this problem before but this is a new strain for me ( Sour Deisel ). I'm using house and garden hydro nutes at the recommended dosage. I use de-i water and my ppm after adding nutes is about 1200, pH around 6.0. I use Green Trees ebb and flow system using the little red or brick colored balls for medium. I'm watering twice a day and my light cycle is 19 on 5 off. 1000 watt MH's about 3 1/2 feet above the plants. I thought it might be a Mg deficency but I need some advice . Thanks for any comments

you can some try some iron.. and do 18/6