How much storage solution do you use and do you change it each time you use the device? New to this. Thank you.

I do not change it every time I use the device. I rinse my probe of in distilled and shake/pat dry. The kit come with a storage cap. It has a fill line. I was told on the phone by apera that if storing in the case fill to about half way to the fill line and make sure probe is wet. It's only a few Ml in the cap. I normally top it off when needed but the bottle should last you a very long time. I use it to refill the small bottle in the kit. It's not completely air tight so you may find some solution crust around the top of the cap from time to time. just clean it and you should be good. I am using my meter 3-5 times a week now and have only used about 1" of solution out of the bottle in two months.

Is this solution only used for long term storage, or short term as well? Is there a need to recalibrate after storing in this?

You have to calibrate the meter weekly; if storing longer, calibrate it before use. the solution is good until the next time you use the meter.

This states to use storage solution when not in use is a recommended practice, what is the "recommended practice" as it does not state on the PH20?

It is recommended in the PH20 instructions to use the Apera product (Kaliumchlorid) to store the PH20. That is, fill the container (probe protector) to the line with the Kaliumchlorid liquid, and insert the probe into the protector. I store the AP20 in its case and on its side (probe pointing down) to insure the probe is in the liquid. This also prevents liquid from leaking out.

Is the solution placed in the cap of the PH20 meter?

We now store the cap with water droplets to maintain a modest humidity in the cap. In this way, the probe is ready for its first customer, and they can choose whether to store in 3m KCl or use an alternative method.