Yes PH needs to be the last step before pouring.
One thing I suggest to those with wells is test it annually at least, we just dont know what the oil people have put down there. My well water is slimy and is now acidic setting in that lime layer (should be alkaline), but it PHed at 5.4. I am prepping some concrete to go down it. Another well I have the water is orange (shallow well), another is sulfur (very deep well some 5000 feet plugged at 450), and one that was good last time it was used (shallow well about 25 feet). Other wells here came out with salt, and 1 they told them to plug it, never use it. These wells are not far apart.