I have lots of flagstone in my build - flagstone coping and flagstone beach entry. Many people have talked about sealing flagstone with SWG pools due to problems with spalling/deterioration of the flagstone related to the high salt levels. I do not have a SWG and use TFP method with bleach, so I did not worry about applying a sealant to the flagstone. I started thinking recently about salt build up over time - my fill water is fairly salty at 600 ppm, and I know that bleach adds a bit of sodium over time. Does anyone know of a specific level at which sodium becomes a problem for flagstone? It seems plausible that within a few years I could be approaching SWG levels of sodium in my pool, and I'm wondering if I should consider a partial drain and refill at some point if the sodium levels get too high.