ok so i got this SunGro Sunshine Mix #4 3.8 Cu Ft Compressed Professional Growing Mix | SUGRMIX4
then i got this
Milwaukee Instruments Waterproof TDS Tester Meter Auto Temp Compensation T76 this was 55 on walmart sold direct from the company not walmart
now do i need certain type of chemicals to use to calibrate this ? it says it does it by its self but i heard they can go off
then i got this
Milwaukee Instruments Waterproof TDS Tester Meter Auto Temp Compensation T76 this was 55 on walmart sold direct from the company not walmart
now do i need certain type of chemicals to use to calibrate this ? it says it does it by its self but i heard they can go off