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Ezzo.I'm going to stick my neck out here and suggest that for pools, you'd aim for 1-3ppm (mg/l)and for spa's / hot tubs, due to increased temperatures, and bather to water ratio, you'd aim for 3-5ppm (mg/l).I think the Bestway tester you have is for pools as it's showing the ideal Chlorine level to be between 1.3 and 1.8 ppm.