not sure how to answer. I just follow directions and try not to reinvent the wheel. Personally I would use the solutions offered by the pen manufacturer.
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You would be better off with calibration solution.
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That looks like the felt from the cap of the ph80 in the first pics.
You need to calibrate the pH meter to the manufactured value of the standard. Depending on the resolution of your meter if your standard is 6.86 that’s either 6.9 or 6.86 if your meter is good to the hundredth of a pH unit.
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I highly recommend that Blue Lab TDS pen, I’ve been using one for 5 years with zero issues. My Apera 20 PH pen is accurate and reliable as well 
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