Reef Chemistry 101
Calcium – CA
Calcium is a crucial element on the natural reef, and in fact is a building block of the reef itself. Many corals, as well as invertebrates, clams, desirable algaes, and other creatures on the reef depend on adequate calcium being available to them in the water.
PH is simply a measure of the relative balance of hydroxide and hydrogen ions in water. In layman's terms, this means that there are hydroxide elements and hydrogen elements in the water.
Solutions with a pH measurement above 7 are considered "base", while those below 7 are considered "acidic" and Seawater pH is typically about 8.0 - 8.5.
Alkalinity – DKH
Alkalinity, in short, is the water's ability to withstand additions of acids, without changing the pH. Other terms that are commonly used to describe alkalinity include buffer or buffering, DKH, meq./ltr., and carbonate hardness . The elements that provide this effect are carbonates, mostly sodium carbonate and sodium bicarbonate. Alkalinity is necessary in the aquarium to help guard against large swings in pH, which will stress the tank inhabitants. Recommended idea levels for a reef aquarium is 8 dkh.
Magnesium – Mg
Magnesium is another player in the dance with calcium. Magnesium levels are typically pretty stable in the aquarium, and are easily maintained with routine water changes. However, if calcium precipitation occurs, or the hobbyist does not do regular water changes, magnesium levels can decline. The recommended level of magnesium in the aquarium is 1300 ppm to 1500 ppm.
Kalkwasser (lime water or calcium hydroxide)
Kalkwasser, or "limewater" is actually calcium hydroxide and when mixed properly, it is highly saturated in calcium, and leaves no other residues in the aquarium. It helps to increase calcium availability to aquarium inhabitants and it helps to maintain alkalinity in the aquarium.
When properly dosed, kalkwasser can be used as a tool to gently increase pH to more desirable levels in the aquarium. This is useful in combating the natural trend in closed systems of preventing pH decline.
Iodine is a one of the key component of seawater that has long captured the interest of marine aquarists , as it has been identify as one of the key elements in mainting proper growth and colorization of corals , invertebrates and algae. There are basically two forms mainly ; Iodide and Iodate.
Ammonia - NH3
Ammonia is a compound with the formula NH3. It is naturally created by the decomposition of food by micro-organisms in water and is also eliminated by the gills and in the urine of fish. Ammonia is toxic to fish and understanding it is critical to setting up a healthy tank.
Ammonia can either be in the form of ammonium or ammonia depending on water pH. Below a pH of 7 there is a higher ratio of ammonium to ammonia. Ammonium is less toxic to fish than ammonia.
Nitrate is an ion that has long dogged marine aquarists. The nitrogen that it is formed from comes in with foods, and in many aquaria it builds up and can be difficult to keep at natural levels. A decade or two ago, many aquarists performed water changes with nitrate reduction as one of the primary goals. Fortunately, we now have a large array of ways to keep nitrate in check, and modern aquaria suffer far less from elevated nitrate than they have in the past.
Nitrate is often associated with algae, and indeed the growth of algae is often spurred by excess nutrients, including nitrate. The same can be said for other potential pests in aquaria, such as dinoflagellates. Nitrate itself is not particularly toxic at the levels usually attained in aquaria, at least as it is so far known in the scientific literature. Nevertheless, elevated nitrate can excessively spur the growth of zooxanthellae, which in turn can actually decrease the growth rate of the host coral. For these reasons, most reef aquarists strive to keep nitrate levels down in order to maintain a near to nature ocean condition.
It is part of the "nitrogen cycle" that takes place in most aquaria, and so is one of the first encounters that many aquarists have with their aquarium's chemistry. The marine aquarium hobby is replete with commentary about nitrite, some of which is, unfortunately, incorrect or misleading. Its toxicity in marine systems seems to be far lower than in freshwater systems. This difference is striking, with some of the most sensitive freshwater species being more than a thousand times more sensitive than typical marine species.
Oxidation-Reduction Potential (ORP) is a measure of the relative oxidizing power of the water and is often used as a measurement to determine how much oxidation or reduction reactions are taking place in the water at the existing conditions. In simple terms, you can look at ORP as a pollution index since polluted water has a lower ORP reading.
Phosphorus is one of the basic building blocks of living matter. It is present in every living creature, and in the water of every reef tank. Unfortunately, it is present in excess in many reef tanks, and that excess has the potential to cause two big problems for reef keepers. The first is that is can drive excessive growth of undesirable algae. The second is that it can directly inhibit calcification by corals and coralline algae. Since most reef keepers don't want either of these things to happen, they strive to keep phosphorus levels under control.
Fortunately, there are some effective ways of keeping phosphorus concentrations to acceptable levels. Unfortunately, the means for testing for total phosphorus are not trivial. One can readily test for one of the common forms of phosphorus in reef tanks, inorganic orthophosphate, but testing for organic phosphorus compounds is considerably more tedious. Moreover, if there is an algae "problem", then the algae may be consuming the phosphate as fast as it enters the water, masking the issue. Consequently, reef keepers may not recognize that they have a phosphorus problem, only that they have an algae problem.
There has been a great debate for years on whether one can/should run activated carbon in a reef tank. The anti-carbon argument takes the position that carbon removes beneficial material that coral and other inverts consume.
Carbon is used to remove dissolved organic compounds from the water. The effect of DOCs could be to merely cause the water to take on a yellowish appearance they can consist of complex organic toxins produced by the creatures in the tank. Dissolved substances are not directly absorbed by higher animals and are mainly consumed by bacteria and algae. Coral, anemones and similar critters don't directly consume dissolved organic materials. The zooxanthellae in corals don't benefit much from dissolved organics as they get their nutrients directly from the coral and the uptake is extremely fast. It is highly unlikely that running carbon 24/7 removes any material that is essential to the livestock in a tank. Carbon improves water quality and reduces bioload on the tank.
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