Thanks! Your method sounds pretty accurate, I'll try it out.Friend I love your determination and persistence. I agree that those probe meters are inaccurate and will give false readings. If you want to get a pH meter for liquids you can test the discharge with accuracy.
I use a triple beam scale to weigh my small cups to know exactly when to water. I weigh the cup dry and write the weight on top of the cup. When the weight gets to 20 gram to the dry weight I water again. Its very tricky and easy to over or under water when trying to water by eye.