Small yellow spots

And btw, if you've not grown in DWC before and don't know what the roots can be, take a look at the video in this week of my diary... and keep in mind this is a poor girl that I BADLY stunted in her early life... the second Bruce Banner I'm growing, HER roots are so massive they've taken on the shape of the bucket itself (and you can see a still shot of the roots in the last week's entry for her - wanted to capture the size of just ONE root).... now try to imagine 4 plants in that one pot... growdiaries.com/diaries/152783-grow-journal-by-growinggrannie/week/857360

The small yellow/white dots are the sign of some leaf-sucking insect, probably aphids or spider mites - not thrips... I'd get some Dr. Zymes Eliminator or some Spinosad and use as directed... on ALL the plants in the tent. I, too, think you've packed your tent a bit too much... and will struggle - and I'm not sure of a number of other things here: why are you growing 4 plants in one net pot? Why are you keeping the peat so wet - second photo shows the water level is above the bottom of the net pot and the peat pots are sitting in it? In DWC, it's imperative you keep the water level about 1/2"-1" below the bottom of the netpot - the roots needs that high humidity break from the water itself. You're going to drown your plants!! Good luck!

Your at the top end of your ph for veg cycle. Best kept at 5.8 for veg, 6.2 to 6.3 for flower time. 4 plants for 1 planter will smother things out. 1 plant can get massive in a proper water grow. Roots will suffer with 4 plants and you will have to do so much defoliation, there won't be much power left for the plants.