i agree with daddy. its your testing equipment. get a good ph meter and ditch the liquid. ph meters will last a long time if you take care of it. i have a hanna (which i dont like) that does the job and i only had to recalibrate it once in 2 years. the calibration solution is cheap too. probably $3 for both ph4 and ph7 calibration fluid. temperature of water can screw up test strip or liquids because they dont have a temp compensation built into it.