Rick,

The test for Calcium Hardness found in most pool test kits does not test for Total Hardness which includes Magnesium in addition to Calcium. However, Total Hardness kits are also available. You can also roughly estimate Total Hardness by multiplying Calcium Hardness by 1.4 though that is only for typical mountaing spring sources of water and not mixed sources that have well water -- it's best to get a Total Hardness test kit.

Richard