Do you mean week 2 of 12/12 light cycle? Looks like you might have spider mites. Some times changing the light cycle will bring those little bastards on.(happened to me a couple of times)....Get you a Shell No Pest Strip or two (the active ingredient is Dichlorvose) and hang it in your grow room....Does the trick for me.
Also, you might have that 400 watt light a little too close to the plants....Notice the rolled up edges on the leaves? If nothing else, I'd say you got some heat stress going on.
What are your temps?...How about ventilation?...Got any moving air in the grow room?
The MG ain't really all that bad...You just gotta be careful how you feed.
PEACE.............J