leaves dryin up???????

hey guys, i started my hydros and theyve been doin good so far but im startin to get a problem... some of my leaves are turning yellow and gettin brown spotts on them and they are like crispy i dont know if it is that the light is too close or i need to change the water in the dripper system my 400 watt hps is like a foot and sum inches away frum the plant but i still have no clue help me out guys pleezzz!!!!

How old are they?
Do you have pics?

got a pic?
How often do you change the water?
How ofter do you PH the Res, between changes?
How rich are you mixing you ferts?

ther like 4 to 5 weeks old and i havent yet changed the neuts yet im doin that tomorro how often should i change the neuts???

change it....
Check the PH it is probly threw the roof.
Change it every 2 week but keep an eye on it threw out.

alright dude thanks much.