Downsides to salt pools

[chem geek]

If the ability to lower the SWG output at higher CYA levels is during the day when there is sunlight, then the CYA protection mechanism would account for that. It's not necessary for the SWG to be more efficient -- if chlorine usage dropped due to more protection from CYA (even at higher FC levels) so less breakdown from the sun, then the SWG output can be turned down.

The reason I originally didn't think that CYA protection was the reason was that I trusted the industry chlorine half-life vs. CYA graph which did not account for the significant lowering of SWG on-time one can have at higher CYA levels. However, if this graph is wrong and CYA protection dramatically increases at higher levels, then that will result in the same ability to lower SWG output (level or time).

You can do a similar experiment as Mark did by running the SWG at night and seeing the rate of increase in the FC level at different CYA levels -- essentially just repeat what you are seeing during the day, but do it at night instead (or during the day with an opaque cover that protects the pool from sunlight). If you find that the rate of FC increase doesn't change with CYA level, then there is no change in SWG efficiency with CYA and the reason for the ability to lower the SWG level is just due to a lower rate of chlorine usage. Definitely let us know if you come up with different results as that would indicate a more complex scenario -- possibly a dependency on specific model of SWG.

Richard