What's happning to my plant?

I'm startin to worry a bit now as the leaves on my plant are starting to look very ill. I'm new to growing and don't know what to do right now.
On the bottom the leaves look over fed, curling up and becoming dry and crispy. Should I cut them off or just leave them for a week or two?
I'm using a 600w HPS (not air cooled) which was 33" away form the top of the plant but now i've moved it to 40". Still in 18/6. Just done a 24hour flush with plain RO water. Growing in a waterfarm.
Germd on 11/11/11. Does she look ok?

its burnt up looks like

Crispy nitrogen burn.

Will it be ok? Im going to flower in the next week and just woundering will it pull through?
Everything else seems ok like she's still taking up water. Might just cut them leaves off in the next few days when they start to die off more.

Hey palits like nut burn and really N def.Flush asapthe plant look awesome in top.