I used a solution tester kit. It's for hydro, but what I did was water and caught the water from the bottom, then dropped in the pH testing solution. I did that when I first started 3 weeks ago and then again a few days ago. The first time it was light green which according to my chart I'd say was around 6.6 or 6.7. The last time I tested it was like a light yellow, almost too clear to see. I'd say it's now in the 6.2 to 6.4 range.
The soil is promix but it's been sitting around in big ass freezer bags for like two years sealed up so I don't know if that would hurt it or make the ph degrade faster towards the acidic side.