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Healthy small polyp stony coral.
The goal of every marine aquarist is to maintain water quality and chemistry as close to natural seawater as possible. In addition research has shown that in the home aquarium water quality can be tuned to either accelerate coral growth rates or enhance coral colouration. One must also strive to keep the water parameters at consistent levels. This is true for any type of reef or fish only tank. Rapid changes in temperature, pH, alkalinity, salinity or other water parameters will put undue stress on the animals. Some organisms are more sensitive than others but nevertheless once an organism is stressed, it is more susceptible to disease and parasites. This may and often will spread to more hardy animals. Below is a table of natural seawater parameters along with our recommendations for accelerated coral growth or enhanced coral colouration parameters.
CALCIUM, ALKALINITY AND MAGNESIUM IN THE MARINE REEF AQUARIUM
Calcium (Ca), Alkalinity (kH) and Magnesium (Mg) are inter-related, and optimum levels are essential for optimum coral growth. If not maintained at or near optimum levels marine animals, corals and fish will not grow, become stressed and can even die. Ca, kH and Mg are the primary ingredients in creating calcium carbonate (CaCO3) which is the skeleton of LPS and SPS corals. Coral Science manufacturers reagent grade reef aquarium supplements to allow marine aquarists to keep alkalinity, calcium and magnesium levels in check. To ensure you have a proper balance it is extremely important you do regular tests of you levels with a quality test kit like Red Sea. To keep things simple we recommend using an automatic 3 channel doser to supply your reef aquarium with the proper balance of Ca, KH and Mg.
Calcium is one of the major cations in seawater. Natural seawater has calcium levels around 420 parts per million (ppm). Changes in water salinity will cause calcium levels to fluctuate. A calcium cation carries two positive charges in seawater and is written as Ca++. Calcium is very important in a reef aquarium as many marine organisms, including corals and coralline algae, use it to create calcium carbonate skeletons. If it is not maintained at adequate levels, such organisms become stressed and can even die. Calcium levels between 360-470 ppm are necessary for good coral growth. A good indication of proper calcium levels outside a calcium test kit is the rate of growth of coralline algae. At Coral Science, we keep our levels at 430 ppm and find that the hardest part of maintaining a reef aquarium is cleaning the coralline off the glass in our display tank! Boosting the calcium concentration above much higher that natural levels does not enhance coral skeletal growth. Experiments on several small polyp stony (SPS) corals have shown that low calcium levels below 360 ppm will limit coral and algae growth Levels above about 470 ppm do not increase coral calcification. In fact uncontrolled, measured additions of calcium to your reef you may do more harm than good as it will precipitate (come out of solution) and foul your water pumps tubing and heaters.
Alkalinity is a rather complex measurement of carbonate anions. Sodium hydrogen carbonate (NaHCO3-) is what corals take up and metabolise into calcium carbonate (CaCO3-) in order to build their aragonite skeletons. Normal to high alkalinity levels imply an adequate carbonate level, whilst low alkalinity levels imply that carbonates are in short supply. Without the regular addition of sodium hydrogen carbonate or regular water changes aquarium water can rapidly become depleted of these essential carbonates. Alkalinity depletion from normal to unacceptable levels can be rapid only taking a day or two in some reef aquariums. This generally takes longer in reefs with a lower demand for carbonate. A reef with only soft corals will require much less carbonate than a reef with clams, small polyp stony (SPS) or large polyp stony (LPS) corals. When the aquarium's carbonate levels are depleted, corals that deposit calcium carbonate can become stressed and with very low levels even die. Here at Coral Science, we recommend that reef aquarists maintain an alkalinity level of between 7 dKH and 13 dKH (125-232 ppm calcium carbonate equivalents). Natural seawater has a KH of 7-8.
Magnesium is the third most abundant ion in seawater. It is involved in a large number of biological processes within all living organisms. Uncontrolled additions of Magnesium and other supplements without constant monitoring and testing will exasperate a chemical imbalance and often do more harm than good. Natural Sea Water has Magnesium levels of 1280 ppm. Coral Science recommend keeping levels between 1280 ppm and 1390 ppm. Magnesium in seawater is a cation that carries two positive charges, just as calcium does. Generally magnesium is a free cation, with only water molecules attached to it. Proper levels of Magnesium are important because it stabilizes the level of carbonate in the aquarium and allows it to be present in far higher concentrations than it would be in freshwater. This allows seawater to act as a buffer for pH within the range of 8.0-8.5. This ion pairing also keeps seawater pH from getting too high and reduces diurnal pH (daily) swings. Magnesium is also extremely important in the process of coral calcification and many marine organisms (if not all of them) take up magnesium from seawater.