Is this a Mg problem?

Hi all, hope someone can help. This is my last living Soma Lavender plant.
Little history: 12/1/09 took cutting, transplanted to 3â?� pot and DWC when rooted, 12/19, over fertilized, almost killed them all, since 12/29 it has been in DWC with plain water. Good news is roots are looking good, but the leavesâ?¦not so good.
Info: DWC system, Tap water ppm=70, pH=9.5 (I adjust it down to 5.8), temp=68-75, water temp=65, Humidity=10-25, I use G.H. 3-part Flora series.

I tried to do research on my own but I want to get it right and would like some opinions/suggestions.
#1 Is this a Mg deficiency? Is Epson salt the cure? If so, how much per gal?
#2, Is it time to start the nutes again? Maybe a 3-2-1 mix at 300ppm? Or another value? Other additives?
#3 Is my water temp, humidity, tap water ok?

Thanks guys for any help you can give.

Warm that poor little plant up. Take it and put it in a good potting soil and place it on a warming pad. You may be too late. That is one sick little plant.