I've never really though too hard about it. I always thought 7.8 was too low. Is that a pretty typical pH? I always try to stay between 8.1-8.3. My SPS do not like 7.8.
I found this interesting articles:
A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH by Randy Holmes-Farley - Reefkeeping.com
Here is an excerpt:
At low pH (say, 7.8), much higher concentrations of calcium and alkalinity can be maintained in solution than at higher pH (say, 8.5). For this reason, aquarists whose aquaria are low in pH often claim that they have no problem maintaining high levels of calcium and alkalinity, and rarely remove calcium carbonate from their pumps, while other aquarists with much higher pH do not understand why they cannot maintain such conditions in their aquarium, or why their pumps often rapidly clog. The effect of having more carbonate at higher pH is one of the main drivers of that difference (the other being that many corals may actually demand more calcium and alkalinity at higher pH, as
they can calcify faster at higher pH). As a follow up, do not assume that low pH is better because it allows easier maintenance of calcium and alkalinity, and clogs pumps more slowly. It is also more stressful for many calcifying corals simply because they have a harder time calcifying at lower pH. That increased difficulty is due to the fact that they have to
pump out a proton (H[SIZE=-1]+[/SIZE]) when they make carbonate from bicarbonate, and the lower the pH, the more H[SIZE=-1]+[/SIZE] already in solution, and the harder it is to pump out the additional H[SIZE=-1]+[/SIZE].
