How fast is she losing leaves? Are you seeing the yellowing move up the plant starting at the bottom or are the older leaves turning yellow at the same time regardless of where they are on the plant?

When you water.....how does the water look coming out the bottom? Is it pretty normal looking, or real brown or yellowish?

http://boards.cannabis.com/plant-pro...hy-how-do.html

Check this thread out......and consider a flush if you think you may have overfed and/or if your ph runoff is below 6.2 (its on the edge right there of soil).

But again...losing SOME larger, older leaves is normal. Sorry I can't figure it out but hopefully someone else knows and will chime in.