What about salt water? I mention this because my cousin has an inground pool (built for the dogs!) and she did it as salt water pool ... but they have it at a really low level ... apparently, it's healthier than chlorine ... and it's supposed to have healing components ... I have no idea ... but you could look into it.
Or others on here might have more info ... good or bad!
Marion’s Zoo-Kyleigh, Raylan-cat, Echo-TAG,