Getting my H2O down to 6.0 PH is raising my PPM by 325ppm !!! HELP PLEASE!!!

I am using GH PH down. Can anyone recommend a PH down product that will not raise ppm so far. I am concerned about too much salts, too low nutes. THANKS

Water (tap) 85ppm, 7.1 PH
Temps are constant 70F H2O, 80F Air.
GH 3 part nutes
Hydroton grow medium (very well rinsed)
I am running a 16 bucket DWC- 45 gal res -- 240 gal per min recirc. pump, 120 liter per min air pump (lots of bubbles), Water Farm drip collars on 20min off 20 min. 6.5" bucket lids, 5 gal buckets, 1k HPS Hortilux. 2 weeks into veg. White Widow & Gods Gift