PH of water

The day before yesterday i did a test testing the PH of the water.Each time i went to take a new reading i wrote down the probe to see if i contaminated it and also for curiosity to see if my results rose from the results from the probe.
PM: Stands for the probe reading.
PH: Stands for the PH reading.
Sample 1.
PM: 4.12
PH:6.46
Sample 2:
PM:4.14
PH:6.43
Sample3:
PM:4.15
PH:6.27
Sample 4:
PM:4.16
PH:6.25

I then wanted to test the second time, the results were:
Sample 1:
PM:4.15
PH:6.46
Sample 2:
PM:4.16
PH:6.44
Sample 3:
PM:4.21
PH:6.31
Sample 4:
PM:4.21
PH:6.32
I then noticed that i had enough time to test the PH for the third time.
Sample 1:
PM:4.21
PH:6.44
Sample 2:
PM:4.22
PH:6.41
Sample 3:
PM:4.24
PH:6.29
Sample 4:
PM:4.28
PH:6.56