Calcium and Alkalinity: Methods to Achieve Proper Levels

One of the aspects of keeping small polyp stony (SPS) corals that is starting to gain significant attention is the need to supplement calcium by the easiest means possible. Before stony corals were maintained, little attention was paid to maintaining the proper level of calcium. Water changes and the dissolution of the calcium substrate were thought to be able to keep the levels high enough, so that no additional supplementation was utilized.

When the Berlin System for keeping corals was introduced in the late 1980's, the concept of supplementing calcium in the tank was first described. This was important, in that prior to this series of articles, little attention was paid to the coral's need for calcium in order to thrive and grow. Initially, the only method described was that of using calcium hydroxide dissolved in water (kalkwasser) to replace evaporated water. As tanks became more sophisticated and stony corals and clams became the dominant animals in these tanks, more sophisticated methods for maintaining calcium levels have been developed. Over the past ten years, it has finally been demonstrated that virtually all corals, as well as coralline algae require calcium in order to thrive.

The reason that no single method of calcium supplementation is utilized exclusively is that, to date, no system has proven to be perfect. Despite the shortcomings of these methods, it is still relatively easy to maintain the calcium level in most tanks above 400ppm (parts per million), the level of natural seawater, as long as these problems are understood and managed. It is very important that calcium levels be kept this high, particularly for stony corals, for these reasons:

• If calcium levels are low, the corals will not grow, and what little growth does occur, will result in thin, spindly branches.

• In addition, if growth is not occurring, the coloration of the coral, particularly at the tips, will not be as vivid as when the coral is growing well.

It is necessary to understand the limits of each method of supplementation before choosing a method for one's system. The methods that are currently being employed include:

• Calcium chloride and buffer
  
• Kalkwasser (sometimes referred to as limewater)
  
• Kalkwasser reactor
  
• Balanced liquid or dry supplements
  
• Calcium reactors
  
• Calcium reactor and kalkwasser combinations

I have used each of these methods over the past ten years, so I feel comfortable discussing their advantages, as well as their shortcomings. However, I do not consider myself an expert on calcium supplementation, as I am still tinkering to try and optimize my calcium supplementation system.

Note: In nature, seawater bathes coral reefs in many minerals and elements. Of all the minerals and elements present in natural seawater, no mineral is consumed as quickly or in as large amounts as calcium. Hard corals, which are the building blocks of the coral reef, demand large amounts of calcium to build their skeletons. Providing enough calcium to meet the demands of all the corals, invertebrates, and algae in a closed ecosystem creates a real challenge for the hobbyist.