Depends--I think the TX Holy rock has a calcium base, which means it's highly likely that it will alter your water parameters--hardness and pH. You can test the rock with some vinegar--if it bubbles, then it will, if there's no bubbling, it's most likely inert and will be fine to use. If you're setting up for African cichlids, or other hard water fish like mollies, it will be fine, but I wouldn't use it for a softwater setup.