I have a aero flo 60 running on a timer with level control tubes in runners all the way down and tubes are sloped. my last grow was with same strain direct clones I ran deeper in the tubes had nutrient constantly circulating my PPM were at 850-1500 Veg- flowering.This grow I see leaf curl down at anything over 800PPM Im running at 760PPM now and am 2 weeks into 12/12 I use 15 gal every 3 days when I top off it shows I used 200PPM with the 15 gal. last run the PPM didnt go down that fast.I have not tried to raise the PPM past 760 sence I switched to 12/12 Running the complete line of GH 3 part expert recirculating program .So the Question is would this be normal? and I like to go 2 weeks between Res. changes but it only holds 35 gal. Should I change out weekly, or top off and add nutes at the 350PPM mark? Thanx