http://www.thereeftank.com/forums/f6...ed-160389.html
Some pretty lengthy reading material. Post #42 starts the chat about CaCO3 being a phosphate binder. Took me a few days to get through it all but there is a table of contents for convenience.
If you think about it calcium carbonate sand (aragonite) is the same material as live rock right? Calcium carbonate. Live rock binds phosphates and we need to "cook" it if the live rock was previously in a high nutrient situation. The sand binds phosphates in the same way. Unfortunately we can't cook the sand to remove them.
Interesting quote from that thread which explains what happens when you cook live rock:
"the bacteria in the LR are able to break off the bound phosphates that are attached to the calcium carbonate. (i will hunt down the references for this, though it may be more reading for you all). they then incorporate it into their bodies and bind it. the more phosphates the more bacteria bodies. if you get enough bacteria together they can create a fair amount of force. this force pushes the dead bacterium (bacterial flock) out of the LR where it can then be swept away from the LR. this bacterial flock is heavier then water so it falls to the bottom, or if your water flow is strong enough it can get pushed around until 1) it gets removed by the skimmer or 2) settles somewhere. either in a hard to reach low flow area or your sump/fuge. if this is planned then it is all good. if you have more sand in these areas then not so good. the force that the bacteria exert is known as Turgor. this makes LR self cleaning when it comes to phosphates.
this also can occur in the sand, but the problem with sand is that it is contained on every side but the top. so the bacterial flock formed from the LR and the sand just keeps building up in the sand bed till it just gets full. at the point the turgor is pushing the flock up into the water column is when you are able to get phosphate readings from the test kits".
Greg