Not at all. Large structures have to be cured in water to reduce the alk levels. NEVER use a regular bag of concrete ready-mix. It includes that cheap sand. Always go with 100% high-grade Portland cement powder, aragonite, and water. I can give you some stuff if you want to experiment.It blends in really good now, and I'm sure even better when those corals fill around it. You have been experimenting with concrete rock for a while now. Have you ever noticed any ill effects from it?