As I read all the previous ...

As I read all the previous solutions, they involve getting the water to the surface before treatment. This means that the pumping assembly (lineshaft and turbines, or submersible motor-driven, and piping) is still vulnerable. Pulling pumps and replacing components is expensive, and can result in temporary insufficiency of system capacity. Feeding chemicals down to the pump bowl inlet is possible, but frought with too many risks. You might consider sealing the portion of the aquifer producing the undesirable water, and drilling more wells if the aquifer will supply the required volume of water. Also, consider drilling a test well to see if there is better water in a lower formation. If the latter, you could install a liner through the undesirable formation to seal it off. Good luck. Please let us know how you wind up dealing with this problem.