I use silica because it does not alter the flavor of the water, and silica is so beneficial for the body. It is required for the production of collagen and elastin throughout the body.
I would not use coral. Coral is primarily calcium carbonate, a cheap and poorly absorbed form of calcium. Calcium carbonate, which is also what Tums is made from, will wipe out the stomach acid interfering with mineral and vitamin absorption, and protein digestion. It also allows for pathogen overgrowth in the stomach and allows passage of microbes in to the body through the gut.