There was a change made in reef-pi in v5.3, that's why you're getting this data. As
@elysics mentioned it's from corrupt data over the I2C bus when reef-pi tries to read the pH circuit. My circuit requires I2C clock stretching but the Pi doesn't directly support that so the fix is to slow down the I2C bus a little so clock stretching isn't required, I'm guessing that's the problem.
To fix run the following command to edit the config.txt file.
sudo nano /boot/config.txt
That should have opened up a file. Using the arrow key on your keyboard go down until you see the following line.
dtparam=i2c_arm=on
Under that line type the following line.
dtparam=i2c_arm_baudrate=10000
Then press
CTRL + S on the keyboard to save.
Then press
CTRL + Z to exit.
Now type in the following command to reboot the Pi, after that it should be fixed going forward.
sudo reboot