How long can you keep/store the Cal solutions? They come in powder and you add this to 250 ml of DW. Can you keep them is sealed jars and use multiple times? Thanks
This is what I understand from the various discussions in the Brew Science forum.
Yes, the mixed calibration solutions should be kept in well sealed
plastic bottles, not sure if glass can be used, I've never seen them stored in glass. Keep 'em away from heat and strong (sun)light.
The pH 4 and pH 7 calibration solutions should be good for at least a year, perhaps 5 years or longer.
I use professional calibration solutions that are over 5 years old, with the same result as a brand new one, on a 0.01 pH accurate meter. The expiration date on the bottles is 1 year from manufacture closed, and 6 months after opening. Go figure.
I use (old) 35mm film canisters to dispense the calibration stock solution into. They also have fairly tight caps, so they can be saved as such. Any small bottle or container will do.
The pH 10 (or pH 9.18 in your case) solution, however, will carbonate, picking up CO2 from the air and lose accuracy over time, depending on how many times that bottle gets opened and how much headspace is in there. You could nitrogen flush it after each use to purge most air and thus CO2.
The good news is, when the meter is used in brewing, you rarely ever need accurate readings (far) above pH 7. Since you're only measuring in the pH 7 and below range, no need to even calibrate the 3rd (pH 10) point, especially with cheaper class meters.
Don't pay too much attention to the large advertised temp range. pH readings should typically be done at
laboratory temps (25C/77F) , and it helps if it has ATC (automatic temperature compensation) for the few degrees up or down from the calibration temp.
https://www.homebrewtalk.com/thread...d-temp-corrected-readings.635517/post-8095944and other posts in that thread.
There's also a sticky on which pH meters have passed AJ's stability test.
I have the feeling many (cheaper) meters and probes are sourced from only a few manufacturers, probably in China.
BTW, that meter has 0.05 pH accuracy, but 0.01 pH resolution (the read out).
Probes don't like to be immersed in hot solutions unless they're made for that. In most brew calculators measurements at lab or room temp pH is assumed.