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Sorry I mean the tub that the test strips came in, not my hot tub.
I'm not a fan of test strips but if you can get your hands on the Taylor book, maybe that can help. I believe that Taylor balances water based on the Hamilton Index.If you switch to a reagent test kit, the Taylor 2005 kit has a water wheel to help you balance your water.
Magnesium Hardness--A measure of the magnesium salts dissolved in water--not a factor in water balance.