I used to raise fishing worms and monitored ph weekly. I found those cheap soil testers either didn't work, some were inaccurate or they weren't accurate for long. I went to only water ph meters but a decent one is at least $60. Calibrated with solution 7ph and the other solution was 5ph I believe. In Georgia, the extension agency will analyze soil samples for a fee. You may not have something like that in your area though.