I'd copy, paste and answer the troubleshooting form. The link is in my signature. Playing guessing games is often fun, but your crop is likely looking for a solid solution, not a week of guesswork.

First thought with your description is...how often do you water, and do you let the soil dry between waterings?

I agree..have never had success with soil probes, and you'll want to know the ph of the water anyway. A ph pen is a wiser (albeit usually more expensive) choice IMHO. My next choice after that would be an aquarium ph test kit. Third would be to ask the local aquarium shop to test my water for me. And I doubt a soil probe would never make my list.