Also there is the arguement with whether crushed coral is better than fine sand. Fine sand being the better trapper of gasses and crushed coral being a better trapper of detritus(bad). The better is really the combination of the two. Sand to trap gas and crushed coral to hold the sand down.
I had quite a bit of crushed coral but that is one of my pistols favotrite things to collect so it is now sitting under a large rock and whats left is fine sand.