It is common for people to use crushed aragonite (coral) as a substrate. Especially when new it does contribute to raising hardness and pH. But after a couple weeks it becomes covered with cycle bacteria and less effective at affecting pH. If the pH drops extremely low, it will again raise hardness and pH but probably not enough to keep hard water loving fish happy. Limestone, marble, and calcite rocks are commonly used to provide that same low baseline of pH and hardness. Dead coral would work, but it gradually dissolves in fresh water. Freshwater fish are unaccustomed to the sharpness of coral and sometimes can cut themselves on it. Oyster shells are crushed and sterilized to be fed to chickens. A layer of that is more effective than anything else I know of. If you put two inches on the tank bottom, it will begin to dissolve and you have to add more periodically. Wash it before use to get the dust and sometimes bits of mangrove roots out of it.
Members who are water treatment professionals advise that the minerals cannot dissolve fast enough to live up to the reputation that they raise pH. I have aragonite as substrate and my pH from the tap is the same as that from my tank. Even at the beginning.
If you want to try this anyway just in case, I would use crushed coral in the filters as part of your media. The water flow will help the mineral to dissolve.
I have this too...no impact. If you need to raise pH, I would use baking soda with every water change.