What's the temp of your res?
You should always pH your water/nutes in DWC particularly. your going to more than likely have lockout issues real quick .i suggest do a res change as soon as possible and pH that shit to 5.5-5.8.
H202 will def help with roots
Kinda looks like thrip damage. And aphids can become a problem fast. I'd grab some dr.zymes and fully coat plant and really focus on undersides of leaves
I water just about a gal everyday per plant.granted I'm in 2 gal pots but 4-500ml every 3rd day in early flower is scary low. Your pots must be dry as hell no?