from what i can tell, in the "low demand" tank it starts to do some good around 8.1 ph and in the "high demand" it starts to do some good around 8.15 ph.
Here is one part of it:
"Once we penetrate below the surface of a sand bed or of live rock we encounter an environment chemically different from the ambient aquarium water. In these interstitial spaces high densities of microbes and infaunal organisms (polychaete worms, sipunculans, sponges, etc.) make a living. They draw food from the water column, whether detritus, plankton, or whatever else, into these spaces, digest it, and release CO2 as a respiratory byproduct. As a result, the dissolved CO2 concentration in porewater is typically much higher than in the overlying water column, resulting in lower pH, CO32- concentration, and than in the overlying water column. Because of this local reduction of dissolution of carbonate minerals can occur in sand beds and live rock."
that says that some critters help the solid CaCO3 dissolve by breathing on it under the sand or deep in the rock...
I don't plan on having this be my only buffer, but use it in addition to kalk other additives... besides, having a ph of 7.6 isn't out of the question. last summer my tank in the garage was down in the 7.4-7.6 until i started to do kalk. i didn't have much sand, didn't do many WCs, and didn't add much to my tank... (don't try this. my trumpet did fine, but i lost an open brain)
