For optimal performance, re-calibrate your meters periodically or if testing TDS or conductivity levels in wide or different ranges. The only way to know your TDS meter is giving an accurate reading is to calibrate it often. Foil packs are great but they need to be thrown away after each use. Our Solution measures a standard conductivity of 1,000 ppm and comes in a perfect Perfect Three ounce size!NaCl solution 1000 ppm 3 oz. bottle (88.7 ml) 1 1000 PPM oz bottle of NaCl solution
