I would not waste money on another test for GH/KH as you only need to know these numbers for your source water. The levels from the online data are more likely correct, and as essjay or someone suggested, take a sample of your tap water to a reliable fish store and ask for a GH test. Just make sure you get the number and their unit of measurement; do not accept meaningless terms like "moderate" or "OK," we must know the number.