I had this happen to me once. I tried several different things, cal mag, Epsom salt, but I think the problem was inconsistent watering. I don't think the lower roots were getting enough water. As soon as I upped my water amount the problem went away. I don't give enough to cause runoff but I do like to see some condensation at the bottom of the pot.
putembk Reviewed by putembk on . top leaves yellow/includes troubleshooting form What is your experience level? (first timer, novice, experienced...) FIRST TIME Your Equipment: .1) Type and wattage of lights. (MH, HPS, CFL's, tube fluorescents, LED's) 600W hps .2) Distance from tops? 18-24 INCHES .3) Reflector type? (cool tube set-up, bat wing, enclosed reflector, bare bulb...)COOL TUBE .4) Is there a consistent fresh air supply? YES BUT NOT THE FRESHEST:( .5) Do you have an exhaust fan and a circulation fan?YES .6) What are the bulb wattages, kelvin ratings, and Rating: 5