somebody please help its dying

Can somebody please help....I have 1 plant under a. 150 watt 5000 lumen cfl and using schultz ap plant food 10-15-15 I recently switched it over from a 18/6 to 12/12 lighting schedule and at first the plant was healthy now the leaves are curling under and drying out. I don't think its my watering schedule as I have only watered about once a week or when pot is light and dirt seems to be drying out...what am I doing wrong...is it one thing or many and is there anyway to reverse any damage I've done to the plant?

sounds like the plant isn't getting enough water, put up some pics.

Pics would be great. But whats your temps, ventilation and air circulation look like? Also how big is the plant and how far do you have your light. You have given very little information to work with.

how much nutes did you add?

overfertilization can cause this problem also.

The plant is approx 2 - 2 1/2 ft tall, I have them set up in a 4 ft tall carboad box linned with tinfoil and a small rotary fan set up at the top for circulation with the light about 8 in away. Nuts I've
done exactly what's on bottles instructions its a concentrate plant food so 1 dropper per qrt. Temp wise I try to keep between 70-75

Ill add some pics in the next couple hrs