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How Hard Water Testing Works

          Because water hardness is comprised of two parts (the metal ion part and the carbonate part, both of which are important), test kits for both are available. The simpler of the two types is for carbonate hardness (KH). KH test kits actually donít measure the amount of carbonate in the water, but measure the amount of buffering capacity as it relates to acidification...............

          The test kits that determine hardness derived from calcium and magnesium ions, also known as general hardness (GH) test kits, are significantly more complex. GH tests work by titrating an alkaline (~ pH 10) sample of your aquarium water with a metal-ion complexing agent, usually EDTA.........................

How The Testing Was Done

          Four test solutions were chosen that were known to have total calcium levels and carbonate levels in the range of aquarium hardness test kits. These were: 1) A calcium chloride solution and a sodium carbonate solution, both with 50 ppm CaCO3, 2) A calcium chloride solution and a sodium carbonate solution, both with 100 ppm CaCO3, 3) A calcium chloride solution and a sodium carbonate solution, both with 150 ppm CaCO3, and 4) A calcium chloride solution and a sodium carbonate solution, both with 200 ppm CaCO3. The calcium chloride solutions and sodium carbonate solutions were prepared from anhydrous solid calcium chloride and anhydrous sodium carbonate, respectively, weighed on an analytical balance to the nearest milligram and dissolved in ultra-pure de-ionized water. An example preparation of a calcium chloride solution would be: 100 ppm CaCO3 = 100 mg/L CaCO3 X 110.99 g CaCl2 per 100.09 g CaCO3 = 111 mg/L CaCl2 -- weigh 111.0 mg CaCl2 and dilute to volume in a 1 L volumetric flask. An example preparation of a sodium carbonate solution would be: 100 ppm CaCO3 = 100 mg/L CaCO3 X 105.99 g Na2CO3 per 100.09 g CaCO3 = 106 mg/L Na2CO3 -- weigh 106.0 mg Na2CO3 and dilute to volume in a 1 L volumetric flask.

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