Let's think out side the box here. Think of a Calcium reactor where the pH has to be ~ 6.8 for it dissolve it. Now think of one with aragonite sand in their tank. If it dissolved at pH in the 8's your tanks would look like a clouded mess. If it dissolved at that pH how the heck could corals even grown. When one adds any kind of fresh aragonite to a system the pH, Alk and Ca++ actually all go down due to solution kinetics. This causes over growths, also called surface poisons, on the grains of the aragonite where Hi-Magnesium Calcite grows till there is an equilibrium. Lastly, if you look at aragonite rate constants, i.e, the amount dissolved at x pH over time it is about nil in any kind of NSW pH.
Is it possible at all to get around this...yes. Dissolution rates and precip rates are controlled by the pH Ca++ and Alk. These "rates" are called Omega numbers. If one looks at or calculates these out you will see that the Alk and Ca++ and Alk have to be very low and well below that of any reef tank. For example, it will start to take place with a pH of 8.2, Alk 1 meq / l (2.8 dKH) and Ca++ 340 ppm. If we now raise these to more of a reef tank levels say, 410 ppm and Alk 2.5 meq / l (7dKH) the pH has to be in the mid 7's for dissolution to take place.
The CarbiSea "Chemist" is very confused

They get this 8.2 (actually they claim 8.3), which is not a pH at all but a FW pKs ( solubility product constant to the neg log base 10) value for aragonite. A pKs is a number that tells you how much you can dissolve, to reach saturation, not at what pH it dissolves.
Now for the "touch down". Tests have been run on these powdered aragonites.
Calcium Carbonate as a Supplement
http://www.advancedaquarist.com/issues/july2002/chem.htm