Why is there CYA in an indoor pool to begin with?
HU? Who said anything about an indoor pool?

If it truly does work, I can see where it would be beneficial to use it in an area that has water rationing or restrictions and you have a high CYA. I can see how it would be worth it (even at $50 a gallon) if you didn't want to risk getting high fines for excessive water use in a draught area that has strict laws about that kind of thing (water usage).