When corals and other calcium carbonate builders grow their skeleton organically, a small amount of phosphate which is a basic building block of all living tissue is stored along with some other organic nutrients in that skeletal material. About 15 or more years ago it was common advise to run effluent from a calcium reactor through some type of po4 reduction media to absorb the po4 released from the dissolving calcium carbonate in the reactor. Also consider the the decades of life that has grown died and regrown layer after layer on and in the depth of the rock detritus and sediment trapped in the homes of boring microbes all of these creatures leave their dirt and decomposing waste Life grows on and in, then dies and is grown over and over. Real live rock is not really rock at all but the compacted corpses of decades or centuries of years of life. On the other hand growing coral on dried and cleaned or man made rock can be akin to trying to grow tomatoes in the dust bowl. You can do it but your going to have to manually condition the soil to be successful.
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