25PPM for tap water is quite low.
Are you trying to calibrate an EC/PPM pen or a PH pen?
Using distilled water for calibration of a PH pen is not normally recommended. It is very PH unstable. The only case that I have seen where the manufacturer suggests the use of distilled water for PH calibration is for the super-cheap Chinese models. While inexpensive, those have caused nothing but difficulties.
Distilled water is sometimes used to rinse the probe prior to using a calibration solution. E.g. buffered PH 7 cal solution used for single point calibration. Or, multiple cal solutions (4,7,10) for pens with multi-point calibration. And, never use distilled water for storage of a PH pen.
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