The solution is only to calibrate your meter . put some 800 ppm in a cup . turn on your meter and set for ppm, then put meter in cup with solution . if it reads 800 your meter is right . you need solutions to calibrate the ph too. put solution back and save. Now turn on meter and dip the end in rez. What's it read there you go ppm. The 800 solution is for milwakie tester. You need others for the hanna I have the next step up to ppt. You need different solutions to calibrate that tester.. Some how you got to get online and check them out. Do not put that 800 PPm in your hydro. These meters come pre calibrated. Put your water in rez. Check ppm then add nutes to that number. for veg or flower. then any other additives, check ppm. Wait 5 minutes and check ph. Adjust up or down. 5.9 Is great.