pH meters should be calibrated frequently (every 1-4 weeks, depending on use).
Two-point calibration (using both 4.0 & 7.0 buffers) ensures the most accurate
calibration possible. Do not reuse calibration solution, as once it has been
used, it is no longer sterile and may result in improper readings. Pour a small
amount into a shot glass and discard after use. Suitable for all makes and models
of pH pens and meters.
pH Calibration Solution is available in single-use sachets, as well as 230
ml (approx. 8 ounces.) and quart bottles. We also offer a "twin-pack"
containing one 8 ounce bottle each of both 4.01 and 7.01 calibration solution.
All pH calibration solutions that we offer are made by either Hanna, Green Air
Products or General Hydroponics.