oolitic sand is best IMO as a base layer under aragonite, it creates an excellent anoxic zone for anaerobic bacteria, its my favorite sand for low flow tanks, invert only tanks, bottom three inches of a deep sand bed, and applications as that. its hard to use in a high flow tank as a top layer, or with large/fast swimming fish, or with sand sifting fish as it is small and suspends easier than larger grains.