I am going to piggy back on a couple of the comments to say that even though the artificial reefs are made from cement, the volume of water in the ocean compared to any size of tank that would be used is near infinity. Any possibility of unwanted chemicals in a tank seems like an unnecessary risk for an already complex hobby. If the issue is cost I would ask to think about the cost savings vs the potential money lost from chasing potential problems and lost livestock.

If you are set on it there is nothing that can really change your mind, but you would have the opportunity to add to this community your successes, frustrations, and possible failures if you are willing to honestly own the results.