The medium is Happy Frog soil I pH around 6.7-7 I feed once a week and give it plain water in between. So pretty much in a week i'm giving it plain water once and feeding it once. They're in 5 gallon pots I'm using a 1000 HPSGive us a little more info please for a positive diagnosis. Medium? PH? Feeding schedule? Size of plant? Size of pot? Light being used? Ideally a pic of effected leaf and plant out of hps light. Could be a couple of things wrong but need to see actual colour of leaf and a whole plant shot if possible to see area of effected leaf/leaves.