hey Cameron check out this article by Randy:
pH
Aquarists spend a considerable amount of time and effort worrying about, and attempting to solve, apparent problems with the pH of their aquaria. Some of this effort is certainly justified, as true pH problems can lead to poor animal health. In many cases, however, the only problem is with the pH measurement or its interpretation.
Several factors make monitoring a marine aquarium's pH level important. One is that aquatic organisms thrive only in a particular pH range, which varies from organism to organism. It is therefore difficult to justify a claim that a particular pH range is "optimal" in an aquarium housing many species. Even natural seawater's pH (8.0 to 8.3) may be suboptimal for some of its creatures, but it was recognized more than eighty years ago that pH levels different from natural seawater (down to 7.3, for example) are stressful to fish.6 Additional information now exists about optimal pH ranges for many organisms, but the data are woefully inadequate to allow aquarists to optimize pH for most organisms which interest them.7-11
Additionally, pH's effect on organisms can be direct, or indirect. The toxicity of metals such as copper and nickel to some aquarium organisms, such as mysids and amphipods,12 is known to vary with pH Consequently the acceptable pH range of one aquarium may differ from another aquarium's, even if they contain the same organisms, but have different concentrations of metals.
Changes in pH nevertheless do substantially impact some fundamental processes taking place in many marine organisms. One of these fundamental processes is calcification, or deposition of calcium carbonate skeletons, which is known to depend on pH, dropping as pH falls.13,14 Using this type of information, along with the integrated experience of many hobbyists, we can develop some guidelines about what is an acceptable pH range for reef aquaria, and what values push the limits.
The acceptable pH range for reef aquaria is an opinion rather than a clearly delineated fact, and will certainly vary with the opinion's provider. This range may also be quite different from the "optimal" range. Justifying what is optimal, however, is much more problematic than is justifying that which is simply acceptable, so we will focus on the latter. As a goal, I'd suggest that the pH of natural seawater, about 8.2, is appropriate, but coral reef aquaria can clearly succeed in a wider range of pH values. In my opinion, 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.
That the calcium level is at least 400 ppm. Calcification becomes more difficult as the pH and calcium levels fall. It is not desirable to push all of the extremes of pH, alkalinity, and calcium at the same time, so if the pH is low and cannot be easily changed (as may be the case in an aquarium with a CaCO3/CO2 reactor), at least make sure that the calcium level is normal to high (~400-450 ppm).
Likewise, one of the problems at higher pH (anywhere above 8.2, but progressively more problematic with each incremental rise) is the abiotic precipitation of calcium carbonate, resulting in a drop in calcium and alkalinity, and the clogging of heaters and pump impellers. If you push the pH to 8.4 or higher (as often happens when using limewater), make sure that both the calcium and alkalinity levels are suitably maintained (that is, neither too low, inhibiting biological calcification, nor too high, causing excessive abiotic precipitation on equipment).
Transient upward spikes are less deleterious than transient downward spikes in pH.
full page:
