#1 - can you reuse the calibration solutions? Seems stupid to just pour them out afterward. But I do because i don't know how stable they are,
You are not supposed to but you can. I do that b/c I’m cheap. I have 500 ml of the 7.00 and the 4.00 buffer and keep about 2 oz of each in the small 4 oz bottles that came with the buffer I purchased from the HBS a while back. About every 6 month I replenish the buffers and the meter shows a difference of about 0.01 – 0.02 between the old and the new.
Buffer solutions are very stable. They are strong buffers and if you rinse your probe with RO or distilled water before you put it into the buffer, you are not adding any acids or bases that could chance the acid/base balance in the buffer.
#2 - Do you need to rinse the calibration solution between tests? I do (with tap water) but was wondering if this skewed the results.
Yes, you have to rinse the probe. And you need to use very soft or distilled water. If you don’t rinse, you’ll get too much mixing of the two buffers over time that it will start to make a difference. Both buffers are strong enough that that they can affect each other. DI water has no strength and there is no problem if you get a drop or two of that into the buffers.
#3 - how exactly do you store the meter? I am currently storing it on the kitchen counter in a Kolsch Stang filled with storage solution to cover the tip. That is a pain though. How much longer will the solution preserve the tip compared to stroing it dry in the case? Seemed to work fine for several months for me. What's the deal?
I build a little holder for my pH meter:
The probe sits in an empty pill bottle filled with storage solution. I drilled a hole in the cap that fits the probe exactly. You want to minimize evaporation.