http://www.reefkeeping.com/issues/2004-05/rhf/index.php. the pH range from 7.8 to 8.5 is an acceptable range for reef aquaria, with several caveats. These are: That the alkalinity is at least 2.5 meq/L, and preferably higher at the lower end of this pH range. I base this statement partly on the fact that many reef aquaria operate quite effectively in the pH 7.8 to 8.0 range, and that most of the best examples of these types of aquaria incorporate calcium carbonate/carbon dioxide reactors which, while tending to lower the pH, keep the carbonate alkalinity fairly high (at or above 3 meq/L.). In this case, any problems associated with calcification at these lower pH values may be offset by the higher alkalinity. So yeah you can have a low pH and an acceptable ALK level. Mr.Randy Holmes-Farley, makes it so much more understandable then I ever could. I partially agree with Guitar in that some tanks do have a chronic low pH that adversely affects the entire health of the system. Those tank types commonly have higher C02 concerntration, smokers, tanks in basements, homes closed up to maintain a warm environment. Correction with buffers alone though can lead to bigger problems then a chronically low pH. Not the best the intervention for newer hobbyist.