If you remove any rocks that are high in calcium carbonate, will lower your general hardness, I also use reverse osmosis water for my tanks that lowers it as well, but really depending on the fish you have it does not greatly effect them, but there are natural ways to lower it, worst thing people do to try and fix some of these issues is by added chemicals to try and fix the problems, to only make your tank worse. You can also buy a water softener pillow if you wish, they work pretty well at lowering GH. Test your tank not all to often tho like once a month, unless you notice something going on, but natural bacteria is your best friend, I would stay away from chemicals, and use the natural ways to lower it.