!!Yellowing Leaves Brown spots..Whats Wrong?!?

Yellowing Leaves with brown spots..mostly on lower leaves but some on top...can some one explain???
Hydroponic System, with rockwool medium..lowered nute strenth just in case......400 watt hps .....4th week of vegetative growth..plz help!

There are a lot of different things that can cause these symptoms. However, with more information and better photos, we can narrow it down.

best camera in my house at the moment.....but you could stil see the yellowing and spots all over..thx

Do you think that it could be over fertilized? temps range from 75-82
air stone added to resevoir for added oxygen

YOU KNOW WHAT I HAVE THE SAME PROBLEM I DONT KNOW IF ANYONE CAN HELP ME here are some pics!!

http://i41.tinypic.com/oti102.jpg
http://i44.tinypic.com/2n00ayu.jpg

THat's a light burn.

looks more like nute lock out