Look closely, even go in and check JUST as the lights are coming on for evidence of splashing (won't evaporate so fast). I'd hate to send you off to throw money at a problem before identifying the true cause.
Yeah, I'd go no higher than 1mL per 20 gallons on the ST. 2 drops per gallon is probably going to be fine for ya. I just suspect you're giving an awful lot of nitrogen to the point of possible overdose.

And a final comment on all this... When I've run hydro, I generally write off any low leaves less than 3-4" from the surface of the media as not only a loss (they get the splash thing for example), but as a liability for air flow and then possible mold/pest problems. I like to see the first couple inches of stem bare so I can access the drip feed and circulate air easily.

And since you have the GH micro, a foliar feed with a VERy weak solution would benefit you right now.