I'd like to build up the bottom of my tank so I don't loose so much of my dry coral pieces in the sand. I'm planning at least a 3in substrate like I did before. Last time I made DIY rock to build up the bottom and it worked really good but it took fooreevvver to cure it. I read somewhere that you can use limestone as a base or as ornamental dry rock. Is this true? If so, I know of a landscaping supply company a few miles away that sells to the public and I know they have limestone slabs for retaining walls in small enough pieces to fit in my tank.