john, the purpose of a DSB is not to buffer the water, the pH would have to drop to a VERY low level for that to matter because it only starts to break down when pH is much lower than what is healthy for our livestock, and then who cares if it buffers anyway.
the dsb serves to convert nitrate to nitrogen in the anaerobic layer deep in the bed. additionally it provides a place for many small organisms to thrive which then in turn become food for reef inhabitants, especially corals and fish.
I am looking into it for the reason that I don't want a BB tank, it's ugly for one, and secondly it lacks a lot of the smaller inverts that the reef needs. I also don't want CC as I have read and also learned from the experience of using CC that is is nothing more than a detritus trap, basically causing massive pollution in the tank. a sandbed requires no siphoning, unlike the crappy CC, it also stays nice and clean and will actually HELP to process waste instead of just accumulating it.
from the reading and discussion I have had with Dr. Ron the main things that are important for a DSB is the sand itself and the organisms in the sand.
first off you have to have the right sand...very small, sugar-sized grain, so that in the lower levels their is very lilttle or no oxygen, that is where the bacteria that convert nitrate to nitrogen live...too big a sand grain and they will not thrive and the bed will not work...by the same token if the bed is not deep enough, at least about 4 inches deep, then oxygen will be present and the bed will not work, at least not to convert nitrate...finally Ron pointed out that most important to the success of the bed is the worms and such that live in the sand...they stir the bed in their search for food...allow small amounts of waste to move down into the anaerobic parts of the bed...they also keep the sand from clumping together and thus allow the nitrogen to bubble back up in small amounts instead of accumulating in the bed itself
so basically the DSB acts as an additional filter material for converting nitrite to nitrate, and also helps to covert nitrate to harmless nitrogen lower in the bed, and also provides food for the tank.
but if you have a sand bed that is too shallow, made of sand that is too large or of varying sized sand, or missing the worms and critters that stir the sand, then basically you are back to what crushed coral is, a trap for waste that eventually leeches that waste back into the rest of the tank
additionally what Ron told me was that you really should probably use argonite sand because it doesn't have as sharp of edges and because it is available in the very small grained size, othlitic sized, that is needed...non-argonite large particle, not othlitic sand is fine for a decorative sand bed that does nothing...but I need the real stuff for a fully functional DSB