Thank you for your question. Choosing the right buffer for your aquarium will depend on the types of livestock that you plan to keep, and at what pH is ideal for them.
According to SeaChem, the manufacture of Marine Bufferâ„¢ and Reef Bufferâ„¢:
Total Alkalinity is a measurement of three main ions: carbonate, bicarbonate, and borate. In saltwater, bicarbonate drives the pH toward 7.8, carbonate drives pH toward 9.1, and borate toward 9.5 or more. Because of the chemistry of buffering systems, the closer you get the pH to the pK of a buffering system, the harder it is for the pH to shift. So, if you blend a buffer so that the combined product drives the pH toward 8.3, then the more you use, the more stable the pH becomes. That is the principle behind Marine Bufferâ„¢. It is a blended buffer that drives and holds your pH at 8.3 because of the blend. The catch to this seemingly simple solution is that most salt mixes contain substantial amounts of bicarbonate salts. This shifts the pK of the buffering system further towards 7.8, and a buffer that shoots for 8.3 will never quite get there. Thus, the pK of Marine Buffer is actually slightly higher than 8.3 in order to combat the influx of bicarbonate at every water change. Marine Bufferâ„¢ was the first buffer on the market which contained borate salts (which make a saltwater buffering system much more stable), and Marine Bufferâ„¢ remains the most effective pH buffer on the market for marine aquaria.
Reef Bufferâ„¢ will also raise carbonate alkalinity; however, it is intended primarily for use as a buffer in a reef system where the maintenance of a pH of 8.3 is often difficult. Competing products are not designed specifically for the reef environment; the pK is too low (in most cases, pK 8.3). At this pK, the proper pH can never be reached in saltwater. Reef Buffer'sâ„¢ higher pK (8.6) allows for greater pH stability in a reef system where the bioload is significantly more than in a fish only system.