It appears from your pics that you just leave a cup submerged in that tub with solution and roots exposed to light, if so then that is your prob. NO LIGHT TO ROOTS OR SOLUTION Put a lid on that tub, put a sheet of the black/white plastic over the lid, cut holes in them both to drop "net pots" in(roots ball up inside of cups and dont escape) and use some nutes designed for hydro and try latewoods formula, maybe a little leaner to start and see how they take it. There is much advice on DWC in hydro section, search recent threads there, get a collective and go from there.........you posted new pics while I was responding...Light reflecting off foil and mylar to under sides of leaves can be troublesome as well