Most high-quality syntheti salt mixes contain buffering compounds that will keep the pH of your water properly elevated. However, several factors can cause pH to drop in spite of the presences of these buffers for example:
1) The waste materials and the byproducts of the metabolic processes of various marine organisms tend to be highly acidic and will gradually lower pH over time if allowed to accumulate.
2) Decomposing food items and the acidic compounds produced during the nitrification cycle will also contribute to this pH-lowering trend.
It stands to to reason, then, that crashing pH levels can be a major problem in an an aquariuam that is overstocked and overfeed. So what can you do to counteract this trend? Obviously, the most important thing you can do is to avoid overstocking and overfeeding, but the next best things is to stay on top of those routine partial water changes! The more often you change the water, the less pronounced the swings in pH will be, even if you tend to overfeed on ocacasion or you fall victim to "one more pretty fish syndrome."
Other factors affecting pH are completely natural and have nothing to do with neglect or poor husbandry on the part of the the aquarist.
1) for instance, certain invertebrates utilize the same elements that buffer pH to build their calcareous shells and skeletons, which effectively reduces the buffering capacity of the water and, hence, lowers the pH.
2) Also, various marine algae, wether cultivated or unintententionally introduced, can contribute to pH fluctuations through their natural photosynthetic activity. Like all plants, algae utilize carbon dioxide and produce oxygen during the day. However, when night falls and the algae begin to produce carbon dioxide instead of oxygen. Since dioxide is acidie, the pH in the auqariuam will tend to drop slightly whenever the lights are turned off.
Again, water changes are the key to overcoming these problems. Frequent water changes will not only help to replenish the buffering agents that are routinely used up for shell and skeleton production by certain invertebrates, but they will also keep the dissolved nutrient level in the aquariuam low, thereby minimizing the proliferation of unwanted algae and discouraging the production of pH-lowering carbon dioxide at night.
