leafs drying up

okay, i noticed a few brown spots on my healthy plants. a week later the leafs became very dry and now have brown tips, some even cracking, but everything was good before. i have been giving them some good organic stuff, wich was working great, but i think there was very little potassium. could this be a potassium def???

someone help my plants are 6 week veg and were looking great a week ago.

pictures? are these leaves at the botton of the plant? sounds like we all need more info or possibly some pictures to help you out.

Yeah pics would be helpful. How far was your lamp from the leaves? Did the leaves ever come in contact with the plant?

heres a pic

the leafs are very brittle, and some new leafs are somewhat deformed, maybe too much nitrogen??