Ph pen madness

Hi, i have 3 different ph pens ( with no manual) all cheap.. 1 yellow/ another green one and a red EZ9908 4 in 1 (the best one)

I have tried calibrating these and they all jump to a different number after holding the CAL button. ( i hopd one in buffer 4.0 and it calibrates to 6.86 automatically after i release the button)

I have no idea how to factory reset any if these and YouTube has drawn blanks.

2 of them were relatively accurate before this messed up calibration (1 is toast) but now it thinks that the buffer 4 solution is actually 6.86 .

Is there any way to manually calibrate these? It seems a bit stupid that its automatic but doesn't work.

Thanks for any info ( i also don't see any screwdriver slot...there is a hole... but nothing behind it...)

Inexpensive, never goes bad, never needs calibration, never wrong........I've never owned a pH meter.
GH drops.

All day.

In 2024, the age of flying cars and space cruises, you guys are using drops?

I have a spendy Aperea combo meter that wont calibrate, using the 15 dollar ph and ppm ones now.


I bought drops but only used them a few times.