You aroused my curiosity about this.
I just added 10 mL GeneralHydroponics pH Dn to 1 gallon of 240 ppm nute solution.
The ppm went up to 970, for a rise of 730 ppm, or 73 ppm per mL of pH Dn (used BlueLab ppm pen).
If added to 5 times as much volume, likely the ppm would go up 1/5 of that, or...