You were right DarkCobra. My tank's GH stopped going up and is now headed back down toward my tap water's GH with water changes. I'm not sure if this was due to the Flourite or something in the old aquarium gravel that sat in a paper bag for 15 years. I had washed the gravel well and it had been previously used in a tank with just plants and fish (no driftwood, etc.). If I ever buy another bag of Flourite, I will hold some out for a test.