[bertoni]

Alkalinity is a topic filled with misleading definitions.

I agree that dinoflagellates, and any photosynthetic organism, for that matter, can deplete carbonate alkalinity, although not total alkalinity. This depletion raises the pH, and phytoplankton growing containers can get very high in pH, up to 10 or so, if my memory is correct.

For most of our tanks, the aeration capacity is high enough that carbon dioxide can enter rapidly enough to ensure that there is plenty of carbonate alkalinity. Any pH below 8.6 or so likely is fine as far as pH effects. A number of organisms seem to prefer to take up bicarbonate for their inorganic carbon, but I don't remember how wide-spread that is.