PH Pen lost calibration in 1 day

[eco-help]

I bought PH Pen (TFTeskits) yesterday I calibrated to 6.86 as instructed
Tap water 7.8
Distilled 7.4
Pool 7.7

today:
Tap 8.1
Distilled 8.2
Pool 8.4
Calibration fluid from yesterday: was wrong too but I can’t recall the value

it doesn’t make any sense what am I doing wrong
I can’t read the PH drop test, pen doesn’t seem to work, can’t read CYA but that’s another story

 

[JoyfulNoise]

Digital pH testers need to be calibrated before every use. Some pH probes are better than others in holding their calibration. The cheaper the probe, the worse they are typically. Also, the probe must be stored with the cap on and the tip must remain moist with whatever storage solution it comes with. If a pH probe tip dries out, it can be rendered useless.

 

[eco-help]

thank you
it didn't come with any storage solution. I received one packet of calibration mix. what is this solution.. I mean is there a specific one you recommend?
Can I use a "known" water like distilled (7.4) or tap (7.8) to calibrate instead of buying the 6.86ph stuff?

 

[JoyfulNoise]

Who is the manufacturer of the pH probe (what brand is it)? The manufacturer should specify what the probe should be stored in.

No, you cannot use distilled or tap water, the pH and dissolved mineral content is too variable. Calibration fluids are pH buffered solutions with very specific pH values that won't be affected by small chemical additions, drag-out, etc. You can purchase bottles of premixed solution (4.5, 7.01 and 10) on Amazon for fairly cheap. You should only need a small medicine cup size of solution to calibrate so a large bottle of solution will last a long time.

 

[ajw22]

Buy pH 7.0 calibrating solution on Amazon. The solution is only good for about 3 months after the bottle is opened.