Topping off your res depends on what your numbers are and what you want them to be at. Did you start at 900 and now the number is 1000? Then top off with RO water to get your number correct.

Did you want 900 and your plants ate your number down to 800? Then you'll have to add more of the entire mixed solution as simply adding one thing like LK or Pro Grow will simply unbalance your nute ratios even more.

I'm sorry if I didn't help sooner but I must say I find your threads full of great info on some things.......and very unhelpful in other ways. You say they are drooping.....got a photo? They could be drooping from overnute, rootbound, too much N, not ENOUGH nutes etc etc etc........ This may be why you haven't gotten very much helpful information in rerturn..

I will say....you are ALL OVER Those numbers!! Good for you and it will serve you well once you get yourself all dialed in.

Good luck.