So here’s my take on what you have. You have what would probably be called lace rock. This type of rock is the exact same as live rock except instead of being taken from the ocean it is mined from areas that once used to be an ocean. The downfall of it not being taken from the ocean is that there is always a potential for contaminants within the rock. Lace rock is a porous carbonate rock. Although it is fine in your Freshwater system you may see you gH values and your kH Values go up. If you do not want your values to go up I would suggest switching the rock for a volcanic extrusive type of rock. This type of rock is pourous as well due to degassing during eruption yet does not alter water parameters. Commonly sold as lava rock.