The process of retaining one substance within another without any chemical or physical interaction (bonding)–in contrast to adsorption. A sponge absorbs water as the water does not bind to the sponge and is easily reclaimed by squeezing the sponge.
Two uses in the hobby. When referring to bacteria (as in aerobic bacteria), it means bacteria which can live or grow only where free oxygen is present. In a more general usage (an aerobic environment), it means an area where free oxygen is present. The opposite of anaerobic.
A measure of the acid-neutralizing capacity (ANC) of water. Acid-neutralizing capacity means the ability to accept acid without a subsequent drop in pH. The more acid that can be added to water before the pH starts to drop, the higher the alkalinity.
Alkalinity is a measure of the buffering ability of water. It is not the measurement of just one substance or ion. It is the combined property of many anions (negative charged ions). To a great extent, the alkalinity of most waters is determined by the amount of bicarbonate and carbonate present in the water. But other substances such as hydroxide, phosphates, silicates and borates also contribute to the alkalinity.
The major excretory product of fish and many other aquatic organisms. Ammonia is formed during the utilization of proteins which the organism receives through its diet. In fish, the majority of ammonia is excreted through the gills.
Ammonia exists in two forms in water, the gaseous or un-ionized form (NH3) and the ionic form (NH4+) which is called ammonium. While the sum of the two forms (called total ammonia) always equals 100%, the percentage present in the water of either form depends mostly on the pH of the water and, to a lesser extent, the water temperature and salinity. For example, assuming a total ammonia concentration of 1 mg/L at a pH of 7.5 and a temperature of 75°F (24°C), the gaseous fraction (NH3) will be 0.0165 mg/L, while the ammonium concentration is 0.9835 mg/L, with the sum of total ammonia equaling 1.0 mg/L. If everything is kept the same except the pH is increased to 8.5, the NH3 value becomes 0.144 mg/L while NH4+ will equal 0.856 mg/L (the sum still equaling 1.0 mg/L).
Ammonia is acutely toxic to fish at concentrations near 1 mg/L of NH3. Chronic low values of ammonia (e.g., 0.1 mg/L NH3) result in stunted fish growth and increased stress which can lead to secondary bacterial infections. The ammonia level in an aquarium should be maintained as close to 0.0 mg/L as possible.
Bacteria whose carbon needs for growth and reproduction are fulfilled by carbon dioxide. Autotrophy refers to the carbon source, not the energy source for growth. Autotrophic bacteria are in contrast to heterotrophic bacteria. The nitrifying bacteria, Nitrosomonas and Nitrobacter are autotrophic bacteria. They obtain energy by oxidizing inorganic compounds, ammonia or nitrite, respectively (see lithotrophic), while reducing carbon dioxide.
A substance that can neutralize a base or an acid so that the original pH of the liquid is maintained or changes much more slowly than if the buffer were not present. Acidity and alkalinity are two measurement of buffering capacity.
A chemical reduction process in which nitrate is converted (reduced) to dinitrogen gas by bacterial processes. Denitrification is an anaerobic process which can eliminate nitrate from water. There are a number of intermediate steps which form compounds such as nitrous oxide (N2O). Denitrification is carried out by bacteria such as Pseudomonas, Alcaligenes and Rhodopseudomonas.