don't flush too much, I've noticed when I flush and re-nute it sort of shocks the plant for a good 6-18 hours

the drooping could be from too much hydration
but you said only 20% of the roots are in the water?

my roots in my DWC are 80% submerged in water with 2 airstones one for each plant

I can't really think of anything

maybe cut down on the H202?