Postby HondaB20B » June 16th, 2013, 11:48 pm
just some things to review again
Salinity
Salinity: 1.021 to 1.025 g/ml fish only, 1.023 to 1.026 g/ml corals
Salinity refers to the concentration of ionic particles in saltwater. The common compounds that are dissolved in sea water include sodium chloride, potassium chloride, calcium and magnesium carbonate, calcium and magnesium chloride.
Measurement: Salinity can measured with electrical conductivity or density. Salinometers, which measure electrical conductivity, show that normal reef seawater is approximately 35% salt particles. A hydrometer or which is much more economical, measures reef water density at 1.024 g/cm3. Hydrometers are glass tubes that contain a weight and a calibrated scale. When they are floated in water, their float level on the calibrated scale can be read to find the saltwater density. Because temperature affects the calibration of a hydrometer, a specific hydrometer may be calibrated for only a specific temperature. A refractometer measures the density of water by passing light through a prism. Light refraction is affected by both saltwater solutes and temperature. Refractometers cancel out the effect of temperature and produce precise and accurate aquarium salinity readings.
Nitrates
Nitrate: Fish: < 50 mg/L, Corals: 0 to 10 mg/L
Nitrate (NO3-) is produced in the marine aquarium by the oxidation of nitrite (NO2-). Nitrate is a major marine nutrient and its depletion limits the growth of all marine algae. Natural seawater nitrate levels are generally very low, just less than 0.5 mg/L. At higher levels than 20 mg/L it may become toxic to invertebrates. Fish are more tolerant of nitrate, but in a fish-only system the nitrate levels should be kept under 50 mg/L.
Reducing Aqueous Nitrate:
Nitrates can be reduced by utilizing algae which absorb it to build their cellular proteins. Refugium filtration systems take advantage of this.
A moderately deep gravel bed (2" to 3" of aragonite 2 to 4 mm particle diameter) facilitates the growth of anaerobic Pseudomonas bacteria that denitrify nitrate to nitrogen gas and ammonia.
Frequent water changes using purified water will also help to keep nitrates in check.
Alkalinity
Alkalinity: 8 to 14 dKH, Ideal = 10 dKH
Alkalinity measures the ability of a solution to resist pH change. Buffers, compounds that react with hydrogen ions (H+) or hydroxide ions (OH-) in solution, are responsible for alkalinity. The primary marine buffers are carbonate (CO32-), bicarbonate (HCO3-), borate (B(OH)4-), hydroxide (OH-), silicate (SiO3-2-), and phosphate (PO43-). The most important is bicarbonate.
Units: Alkalinity can be measured in mg per liter (mg/L), milliequivalents per liter (meq/L), and degrees of carbonate hardness (dKH). Around 10 dKH = 36 meq/L = 179 mg/L. (One meq = the amount of a substance that will supply/react with 0.001 mole of hydrogen ions (H+) ions in solution.) Most test kits monitor alkalinity in dKH.
General vs. Carbonate Hardness: General hardness (GH) is defined as the sum of the divalent cations in a solution. This includes all ions that have a +2 charge: calcium, magnesium, strontium, and trace metals. Because calcium and magnesium are in such abundance in marine systems, the general hardness (GH) is largely due to them. "Carbonate" hardness (KH) is not only due to carbonate, but also to any anion that affects pH. These anions include carbonate, hydroxide, phosphate, silicate, and borate. Most seawater alkalinity is due to carbonate (CO32-(aq)) and bicarbonate (HCO3-(aq)) ions. Carbonate (GH) hardness is considered "temporary" because the carbonates are depleted rapidly by acids.
Excess Alkalinity: It is important not to raise the alkalinity of a marine aquarium beyond 16 dKH. Excess alkalinity will cause calcium to precipitate from the system and crystallize on glass, rock, pump housings, etc.
Phosphates
Phosphate: 0 to 0.3 mg/L
Phosphate (PO43-) is utilized by all cells as an energy carrier between organelles and an information carrier between cells. Phosphate is removed from solution by all photosynthetic algae as they photosynthesize and produce new cells. Free phosphate (PO43-(aq)) is called 'inorganic', while phosphate bound to biochemicals (such as adenosine triphosphate or ATP) is called 'organic'. Phosphate is released into marine aquarium water by the decomposition of organic matter, which simultaneously consumes oxygen.
Sources: Phosphates find their way into aquarium systems in several ways:
Overfeeding: Too much uneaten food in the aquarium is likely the most significant source of phosphate in the water. Decomposition rapidly releases the organic phosphate as inorganic phosphate.
Tap Water: Tap water has phosphates that are often sourced from upstream livestock operations that should never be added to a marine aquarium.
Decomposition: Dead organisms, algae or animals, release phosphates into the aquarium water as they are decomposed.
Low-Grade Activated Carbon: Phosphoric acid used to etch the pores of activated carbon can end up in the marine aquarium. High-grade activated carbon is more expensive - the acids are removed.
Control: While phosphates in sea water are generally around 0.07 mg/L, it is recommended that marine aquarium systems keep the phosphate below 0.05 mg/L. Phosphates can be controlled in an aquarium by either biological or chemical means. Refugiums with high growths of algae and good water flow offer a biological method of phosphate control. Periodic harvesting of the algae continually removes phosphate from the aquarium system. There are also resins and iron reactor systems that can remove phosphate from aquariums systems artificially. These systems generally involve pump water diversion through a tube of resin/powdered iron(III)oxide which reacts with free phosphate. The "cleansed" water is then returned to the aquarium system.
Phosphate Absorption: Phosphates are absorbed by living cells as they multiply to cover rocks and gravel. Their presence indicates a possible phosphate issue. If the phosphate level is initially reduced by water changes and chemical filtration, the bacterial and algal populations that once depended on the excess phosphate will begin to die. As they decompose and disintegrate, they release phosphate and reduce the oxygen levels in the pores of the rock where they grew. This phosphate rebound may produce higher phosphate levels than were initially present before action was taken. Several cycles of water changes and aggressive filtration may be necessary to "permanently" reduce the phosphate to acceptable levels.
Phosphate Adsorption: Phosphates are also absorbed by rock and substrate in an aquarium, and then leached out after its aqueous levels are reduced. Calcium carbonate has a high affinity for phosphate ions. The more porous the rock/substrate, the more phosphate that can be adsorbed. If phosphates are removed from the aquarium water, the phosphates adsorbed onto rock/substrate will leach into the water, leading to a phosphate rebound. Several cycles of phosphate reduction may be needed to "permanently" bring the phosphate to a reduced level.
Adjustment: Phosphates are continually added to an aquarium through feeding. They can be removed by 1) use of calcium hydroxide to precipitate the phosphate from the water, 2) use of a protein skimmer to remove uneaten food and organic material from an aquarium.
Ammonia
Ammonia: All marine organisms: 0 mg/L
Ammonia (NH3) is particularly toxic to living things. In marine systems, most of the ammonia (NH3) reacts with water and becomes an ion, the ammonium ion (NH4+) in an equilibrium reaction: NH3 + H2O <---> NH4+ + OH-. The significance of this is that ammonia is far more toxic than ammonium ions. Higher temperatures and pH favor the formation of ammonia, so these conditions can make an existing ammonia/ammonium ion situation worse. Ammonia concentrations as little as 0.02 mg/L cause stress to fish, while ammonium is tolerated at much higher levels. Ammonia levels must be kept as close to 0.0 mg/L as possible.
Sources of Ammonia: The major source of ammonia (or ammonium) in a marine aquarium is food. High nitrogen foods such as Mysis or brine shrimp can increase ammonia levels beyond the capacity of aquarium Nitrosomonas bacteria to oxidize it. Other sources of ammonia include nitrogen fixation - the reaction of nitrogen gas with hydrogen (ions) by Azotobacter and Clostridium bacteria. A small amount is made by denitrification of nitrate back to nitrogen gas by Pseudomonas.
Reducing Aqueous Ammonia:
Ammonia can be reduced by utilizing live rock and gravel (aragonite) beds to foster the growth of bacteria such as Nitrosomonas and Nitrobacter which will convert it to nitrite and nitrate. Algae can then absorb the nitrate, effectively removing the nitrogen from the aqueous aquarium system. Refugium filtration systems take advantage of this.
Frequent water changes using purified water will also help to keep nitrates in check.
Nitrite
Nitrite: All marine organisms: 0 mg/L
Nitrite (NO2-) is produced in the marine aquarium by the oxidation of ammonia (NH3-). Nitrate is nearly as toxic as ammonia. Its levels must be kept as close to 0.0 mg/L as possible.
Reducing Aqueous Nitrate:
Nitrites can be reduced by utilizing rock and gravel beds to foster the growth of Nitrobacter bacteria which convert it to nitrate. Ay algae in the system can then absorb the nitrate and remove the nitrogen from the system. Refugium filtration systems take advantage of this.
A moderately deep gravel bed (2" to 3" of aragonite 2 to 4 mm particle diameter) facilitates the growth of anaerobic Pseudomonas bacteria that denitrify nitrate to nitrogen gas and ammonia.
Frequent water changes using purified water will also help to keep nitrites in check.
Calcium
Calcium: 380-500 mg/L
Calcium carbonate (CaCO3) is produced in the marine aquarium by the dissolution of calcium carbonate from its aragonite crystalline form. The dissolution equation is: CaCO3(s) <---> Ca2+aq + CO32-aq. The carbonate ion (CO32-) can then accept protons to act as a buffer in the marine system according to the following equation: H+aq + CO32-aq <---> H+aq + HCO3-aq. This is an important reaction - it helps to prevent pH drop from the acids produced by aquarium biological activity. Freshwater systems do not have this buffering ability that marine systems have. Also, carbon dioxide is a "player" in this "calcium reaction system", because it can react with water to form carbonic acid, which can then dissociate to form bicarbonate ions and protons according to the following equation: CO2(g) + H2O(l) <---> H2CO3 <---> H+aq + HCO3-aq. As a result of this, carbon dioxide produced by respiration and decomposition, does cause pH to fall.
Calcium Usage: Calcium carbonate (CaCO3) is a major component of the skeletons of most of the animals in marine systems, from sponges to fish. Reef systems do best at calcium concentrations between 410 and 450 mg/L. Animals cannot grow without calcium uptake from the sea water. The constant uptake of calcium from marine aquarium water by animals causes a constant and gradual decline in the calcium concentration.
Maintaining Aqueous Calcium:
Calcium Reactors: Equipment which consists of calcium-laden materials through which water is passed before adding it to a marine aquarium provides a means of raising the calcium levels:
Aragonite-based systems: Either carbon dioxide-injected water or sulfur-laden water is passed through a reaction chamber of aragonite. The acidity of the carbon dioxide/sulfur-laden water dissolves the aragonite and produces a saturated solution of calcium (CaCO3(aq)). The reactor then passes the solution into the aquarium. This system requires a pH controller to prevent excess carbon dioxide influx, pH drop, and excess algae growth. Cost: over $500.
Nilsen Reactors: Water is passed through a chamber of calcium hydroxide, Ca(OH)2, also called kalkwasser and then passed into the marine aquarium. This method produces high levels of dissolved calcium hydroxide. Calcium hydroxide (Ca(OH)2(aq)) raises aquarium pH and once again is best used with a pH controller. Cost: over $250.
Aragonite Sand: Aragonite (mostly CaCO3) can be used as the substrate of the saltwater aquarium. Its crystalline structure allows it dissociate into aquarium water to help offset the loss of calcium carbonate by animal uptake. It will only help offset - it cannot fully replace - the loss of all calcium from the water of a well-stocked marine aquarium.
Additives:
Kalkwasser (Calcium Hydroxide, Ca(OH)2): Has the highest percentage of calcium by weight, but is difficult to dissolve in water and raises pH. It also tends to contain silicates as impurities, which foster the growth of algae. One positive note: calcium hydroxide removes excess phosphate from aquarium systems.
Calcium Chloride: Is simple to prepare and add to an aquarium without pH deflection. It also quickly produces the desired result of calcium increase. It is so soluble in water, that excess addition is possible. This can cause alkalinity drop which results in a loss of pH buffering, and decline in aquarium pH. Some aquarists caution that excess use of calcium chloride can lead to chloride imbalance - but with the concentration of chloride normally at 19.5 g/L, it would be difficult to create a problem with milligram dosages.
Calcium Carbonate: Powdered calcium carbonate is difficult to dissolve in water. Once a solution is saturated, it will hold no more. It can be dissolved more easily in a Nilsen reactor, without the pH issues of the reactor.
Magnesium
Magnesium: 1200 to 1400 mg/L
Magnesium (Mg2+) is present in seawater at normal amounts of almost 1290 mg/L, much higher concentrations than calcium. One of its primary functions in the marine system is to prevent calcium from binding to carbonate and precipitating out of solution. This is achieved by the bonding of magnesium (Mg2+) ions with carbonate (CO32-) ions so the carbonate ions cannot bind to calcium (Ca2+) ions. This allows the calcium ions to be used by living things in the aquarium. The magnesium to carbonate bond is temporary and reversible, allowing the carbonate to still function as a buffer. The equation for the magnesium-carbonate equilibrium is: Mg2+(aq) + CO32-(aq) <---> MgCO3(s). About 2/3 of the carbonate ions in seawater are bound to magnesium and only 7% are bound to calcium. The reason for this is that the most common divalent ions in the aquarium are magnesium. At around 1290 mg/L - Mg2+ is over 3X more common than Ca2+ Magnesium is often inadequate in synthetic sea salt and supplementation may be needed to keep it high. Ample magnesium helps to maintain both KH and calcium levels. Magnesium is also used by algae to make chlorophyll, and it is a cofactor for a number of enzymes in photosynthetic cells, from free algae to zooxanthellae.
PH
pH: 8 to 8.3
pH is a scale that measures the acidity or basicity of a water solution. Hydrogen ions (H+) are responsible for the properties of acids, and hydroxide ions (OH-) are responsible for the properties of bases. There are always H+ and OH- ions in a water solution because of the dissociation of water molecules according to the equilibrium equation: H2O(l) <---> H+(aq) and OH-(aq). Even "pure" water is not pure - it always contains these ions. The pH scale normally ranges from 0 to 14, with 7 being neutral. Solutions that are acidic have more H+ than OH- ions and their pH is less than 7. Basic solutions have more OH- ions than H+ ions - their pH > 7. Neutral solutions are neither basic nor acidic - they have equal concentrations of H+(aq) and OH-(aq).
Buffers: Marine systems have natural buffers which resist pH change. Buffers are aqueous compounds that cause a solution to resist pH change. The primary buffer in marine systems is the HCO3- ion. As acids enter the marine aquarium from cellular respiration the HCO3- ions react to form H2CO3 according to the following equation: H+(aq) + HCO3-(aq) <---> H2CO3(aq). Unlike freshwater systems that can experience much greater pH changes in short periods of time, marine systems are inherently pH stable.
pH Issues: Aquatic aquarium systems normally experience a decline in pH over time due to the release of acids via decomposition increases the H+ in solution. Carbon dioxide produced by respiration of everything from bacteria to fish also lowers pH due to its interaction with water to form carbonic acid (H2CO3).
pH Adjustment: There are various supplements that can be used to raise pH, such as sodium carbonate and calcium hydroxide. The most important aspect of altering pH is to perform it SLOWLY. Every pH unit of adjustment alters the H+ and OH- ion concentrations by a factor of 10. Marine animals have unusually high INTOLERANCE of pH change. All adjustments should be made by: 1) premixing solutions outside of the aquarium, 2) slow addition of the premixed solution to the marine aquarium.
Iron
Iron: trace: 5.5 x 10-5 mg/L to 0.3 mg/L
Iron (Fe3+) is used by cells as a cofactor for enzyme function. It is a key component of special proteins called cytochromes that move electrons within cell membranes. Iron ions are directly absorbed by algae cells from the sea water. Animals obtain iron through their foods, so aqueous iron is not helpful to them. Absence of aqueous iron will prevent the proliferation of algae and zooxanthellate animals. It's natural seawater concentration is about 5.5 x 10-5 mg/L. Raising its concentration to 0.2 mg/L is not harmful but will encourage zooxanthellate photosynthesis. Iron supplementation may aid in the appearance of zooxanthellate corals and mollusks. If an algal bloom occurs, there must also be excess phosphate/nitrate in the system since they are also necessary for the growth of algae.
