hi guys need some general advise, its my first attemp at this!! so i start from the begining, got a skinny grow tent 4 pot wilma with drip system, 400w with aerowing reflector. im using coco with canna a and b and that cazylum if thts how u spell it! lol. this is my third week and i'm running my lights for 18hrs, and feeding 30 mins every 3hrs i did do it every 15mins per hour but was told this could be the problem. my plants have some leaves which are yellow and dying slighty round the edges. i cut them off a week ago and it seemed to be ok but now i have a few more i'd say 20% of the plant is like it on all 4. ph is at 6 like the guy in the shop told me. i as running at 5.8 but still had the problem!. my temp is about 85 and very hot days can go up to 90 ive just got another fan today to try and bring it down a little. i only use nutes tht it tells me on the table no more no less. cant work it out ?? there 3 weeks old tallest is 10 inch smallest 8! i got them from cuttins but cant find out wat strain they are! please help???? also how long would you advise i stay on 18hr ligt cycle?? thanks!