Two Little Fishies - pH-Balance Marine Aquarium BufferThe pH of seawater in the open ocean is stable, normally between 8.0 and 8.3due to the carbonate-bicarbonate buffering system. In tide pools and aquariums the pH can vary more widely due to the influence of respiration and photosynthesis in the restricted bodies of water. In an aquarium with no illumination it is normal for the pH to drop temporarily due to respiration of CO2 in the absence of photsynthesis. When the lights come on photosynthesis makes the pH rise again. Long-term changes in water quality due to biological activity typically cause a decline in alkalinity and lower pH values. If the alkalinity is low, the pH may not reach the range of 8.1 - 8.4 during the day. Use ph-Balance Marine Aquarium Buffer to raise the alkalinity and Ph to the desired levels and stabilize the water quality in marine and reef aquariums.