Question about adding Epsom salts to Inground pool

[CarlD]

Wow! We get some really interesting questions here! I'd NEVER think to add Epsom Salts to my SWCG pool And I still won't!

[chem geek]

If one uses magnesium chloride in place of some of the sodium chloride, one has to dose it properly. Magnesium has a double charge and is more conductive than sodium. The SWCG cells assume a certain level of conductivity and when they measure salt levels they are really measuring conductivity and translating into equivalent salt ppm (some cells do temperature compensation so report that salt level more accurately at different temperatures). The salt test measured chloride and reports this as ppm sodium chloride. In terms of equivalent conductivity, 3000 ppm sodium chloride is equivalent to ((50.11+76.34)/(106.12+76.34))*(95.211/58.44)*3000 = 3387 ppm magnesium chloride, but if you measure just chloride then you want to measure the equivalent of ((50.11+76.34)/(106.12+76.34))*3000 = 2079 ppm sodium chloride in that test. So it takes somewhat more magnesium chloride by weight to get the same conductivity (it's less quantity on a molar basis) so you target a lower chloride level so keep that in mind when calculating dosages if you still decide to do this.

[CarlD]

Richard, that sounds like an interest theoretical model, but as PoolSean points out, you don't want to try it while your SWCG is under warranty.