Saline in IV bags is buffered to a ph below 7. It is not pure salt and water. There are several reasons for the buffering. We often use saline to piggy back other meds in to the body so we buffer to prevent incompatibility with these drugs. When introducing fluids directly into the blood stream we are usually introducing them in to a vein. The venous red cell is carrying CO2 and slightly acetic itself so we want our IV to be slightly acetic.
Waterbear hit the nail on the head about leaching so we have to give a range not an single value.
There are more reasons but I won’t bore you.
I plan to add salt to my pool as soon I am sure I have my ALK under control.
Steve