pH voltage remains constant in every solution and hence pH doesn't change

I am using the hot tub pH sensor [code](https://github.com/jcallaghan/esphome-config/blob/master/esphome_hot_tub_water.yaml) for pH values but the pH doesn't change with the change of solution.
I had also noticed that this is occurring bcoz of the constant pH voltage in every solution. Can someone help me fix this?