Algae are a diverse group of photosynthetic organisms ranging from microscopic phytoplankton to large macroalgae. Certain kinds of algae called macroalgae can provide many benefits to marine systems in the form of nutrient export and increased stability in water chemistry. Another form of essential microalgae in reef ecosystems is known as zooxanthellae, which are responsible for the photosynthesis that supports coral growth. A third form of beneficial algae is known as coralline algae, which tends to form sheets on rocks with rich colors. Other forms of algae, however, can compete with more beneficial organisms, meaning that algae fall on a spectrum of benefits where some are actually detrimental to long-term tank health.
Alkalinity measures the water’s ability to buffer against pH changes and supply carbonate and bicarbonate ions used in coral calcification. Alkalinity in reef tanks is measured in dKH, and many reef aquaria function between 8–11 dKH depending on the livestock. Stable alkalinity is especially important for stony corals that consume carbonate to grow.
Bacteria are an ever-present element in any aquarium, forming an essential part of the biofilm that processes waste and keeps the system stable. Two important subcategories of bacteria that play a huge role in marine tanks are ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs), and they are collectively referred to as nitrifying bacteria. These nitrifying bacteria turn ammonia into nitrite and nitrite into nitrate, which is less immediately toxic than ammonia and nitrite, but still problematic at elevated levels.
Biofilm is the collection of organisms that grow on the substrates within a marine tank. The biofilm includes nitrifying bacteria and many other small organisms that ultimately help maintain stability in the ecosystem. The biofilm is an essential part of biological filtration, processing waste and converting it into less toxic forms.
Calcium (Ca) is an essential element in marine ecosystems of any size. Calcium provides the basic building blocks for coral skeletons and is required for the growth of coralline algae. Many substrates naturally contain calcium in one form or another, and its presence in the water is crucial for stony corals to deposit their aragonite skeletons. Many reef systems run with calcium levels between 380 and 450 ppm to support coral calcification.
Calcium bicarbonate (Ca(HCO₃)₂) consists of calcium and bicarbonate ions and contributes to coral skeletal growth. Calcium bicarbonate exists only in solution and forms when calcium carbonate dissolves in the presence of carbon dioxide. It is part of the natural carbonate system in seawater rather than a commonly used standalone supplement. It contributes to both calcium and alkalinity in solution.
Calcium carbonate (CaCO₃) is a solid compound consisting of calcium and carbonate ions. It is the main material that makes up coralline algae, coral skeletons, and many natural reef substrates such as aragonite sand and limestone. In reef ecosystems, calcium carbonate exists primarily as a solid structure rather than dissolved in water. Corals extract calcium and carbonate from the water to build calcium carbonate skeletons through calcification.
In reef aquaria, carbonate hardness (KH) is effectively interchangeable with alkalinity and is commonly measured in dKH. Carbonate hardness refers to the alkalinity of the water in terms of the carbonate and bicarbonate available. Carbonate hardness is essential for coralline growth during maturation stages and is consumed consistently in aquaria with many stony corals as they encrust and produce skeletal mass.
Coralline algae is a type of algae that clings to porous, stable surfaces like dry rock. Coralline algae is an incredibly beneficial element of the marine ecosystem because it helps stabilize surfaces and reduces available space for nuisance organisms. Nuisance algae and harmful bacteria have a much more difficult time gaining a foothold in mature systems with developed coralline layers because the coralline occupies much of the surface area that the nuisance organisms need to establish.
Iodine (I) is a sensitive chemical found in reef tanks that is thought to play a role in coral health and coloration, though its exact biological importance is still debated. Iodine is specifically believed to play a role in protecting and enhancing coral color and the growth of soft tissue. However, this element can be toxic if the levels exceed 0.03–0.06 mg/L.
Magnesium (Mg) is one of the most important elements in reef chemistry alongside calcium. Magnesium helps inhibit unwanted calcium carbonate precipitation, allowing calcium and alkalinity to remain available in solution. This ultimately facilitates the stability that reef tanks need to thrive. Some coral frags and other organisms consume magnesium, but the primary role of magnesium is to promote chemical balance in the water.
Nitrate (NO₃⁻) is a derivative of nitrogen produced during the nitrogen cycle by nitrite-oxidizing bacteria. This compound can be beneficial to coral growth in small amounts, but high levels can cause algae blooms and other problems. Nitrate is typically managed through regular water changes and biological export (denitrification, macroalgae, etc.).
Nitrite (NO2−) is a nitrogen compound produced by ammonia-oxidizing bacteria that live within the biofilm. Nitrite is then further converted into nitrate by nitrite-oxidizing bacteria, which can then accumulate or be exported from the system through biological processes or water changes. Nitrite is much more harmful to animals than nitrates, but saltwater animals are generally more tolerant to nitrites than freshwater animals are.
The nitrogen cycle is an ongoing biological process that provides biological filtration in reef tanks. This cycle begins when ammonia is added to a system with nitrifying bacteria and proper circulation, salinity, and stable water chemistry. The nitrifying bacteria, consisting of ammonia-oxidizing bacteria (AOBs) and nitrite-oxidizing bacteria (NOBs), turn ammonia into nitrite and nitrite into nitrate, which is less immediately toxic than ammonia and nitrite, but still problematic at elevated levels.
pH measures how basic or acidic the water of the aquarium is, and should remain relatively stable for successful animal care. Regardless of the type of livestock, pH swings can cause stress and irritation, so it’s important to monitor this parameter regularly. However, unlike many other parameters, problems with pH stability are usually symptomatic of other connected issues. In general, if everything else in your tank is stable, the pH will illustrate that trend. Many reef aquaria run between 7.8 and 8.4 pH, but stability is far more important than landing perfectly on a specific pH value.
Phosphate (PO₄³⁻) is a nutritional element in reef tanks that is produced when food and organic waste decompose. Trace levels of phosphate are typically present in saltwater tanks and benefit many animals, but excess phosphate can stall coral growth and promote the spread of nuisance algae. Extremely low phosphate levels can also inhibit coral growth, so it’s important to maintain proper levels.
Potassium (K) is an essential element present in relatively low concentrations compared to major ions like sodium and chloride. It plays an important role in coral health through coloration, tissue vitality, and cellular function. Reef tanks typically run with around 380–420 mg/L (ppm) to imitate seawater.
A refractometer is an instrument used to measure the salinity of a sample of water. Refractometers record salinity in specific gravity (SPG), and this measurement is affected by the temperature of the water sample.
Reverse Osmosis Deionization (RODI) Systems are water filtration systems that work in 3–5 stages depending on their complexity. Reverse osmosis deionization removes dissolved solids, including chlorine, chloramines, heavy metals, and other contaminants from the water supply to make it safe for reef environments. These systems have individual canisters and cartridges that must be replaced with usage to ensure proper filtration is maintained over time.
Salinity is the measurement of dissolved salt in a body of water. Salinity is one of the simpler parameters to maintain in reef aquaria, but its stability is critical nonetheless. With the aid of an automatic top-off (ATO) system, reefers can maintain stable salinity for weeks or months at a time with minimal maintenance by simply keeping the RODI water stocked properly. Most reef aquaria maintain a specific gravity around 1.025–1.026 to mimic natural seawater conditions.
Strontium (Sr) is a macroelement present in reef tanks that is thought to help stony corals produce and maintain their skeletons. Strontium can be incorporated in small amounts into coral skeletons in place of calcium, though its biological importance is still debated. Only about 7–10 mg/L (ppm) is needed for ideal conditions, and strontium is premixed into many sea salts designed for coral growth.
A substrate is a surface with the potential to host coral, microorganisms of the biofilm, and microfauna as they grow and mature. Substrates that support coral growth come in a wide variety of materials like aragonite, ceramic, cement, silica sand, and more. Substrate quality varies depending on factors like porosity, calcium availability, cure methodology, and stability. Substrates come in varies forms, including frag plugs, frag discs, frag tiles, rocks, sand, and more. At Artisan Frag Plugs, we specialize in creating high quality substrates in multiple forms and natural ingredients.
Trace elements include elements that are essential to healthy coral growth and water chemistry, but are needed in relatively small concentrations. Trace elements typically refer to iodine, potassium, and strontium, and these elements are often replenished in tank systems through regular water changes.
Water stability is perhaps the most essential parameter to maintain, despite its relative nature. Water stability refers to the maintenance of chemical and physical parameters within a consistent range. The parameters that affect water stability include elemental levels; water flow; lighting intensity, wavelength, and photoperiod; filtration, frequency of water changes, consistent salinity, and more. Water stability takes time to master, especially in new reef systems with many microorganisms competing for substrate. The easiest rule of thumb to remember with water chemistry is that most reef animals tolerate stable conditions with parameters slightly outside of their ideal ranges better than fluctuating parameters that are within their ideal ranges.
