If you do use the foxfarms it will lower your PH a big amount. Depending on your source waters PH, that could be a very bad thing. I would definitely suggest getting a PH pen and some PH up/down.

This is a cheap and good one that I use.
Milwaukee pH 600 pH tester pH meter 0-14 NEW - eBay (item 220614445206 end time Dec-26-10 16:19:10 PST)

I just store it in regular tap water and clean regularly. Calibration packets are also cheap.