a good article about ORP in case some bros here wanna know
#Let us start by saying that redox potential is really a saltwater thing, so if you have a freshwater aquarium, read on because we'll explain this soon, or . . . because you like the way we write. In our humble opinion, the redox potential of a marine aquarium is one of the best measures of success in maintaining a great saltwater environment. If we had our way, every salt tank everywhere would be equipped with a redox meter (ORP meter).
We'll start with our very own anthropomorphic, unique, over-simplified and only-partially-correct definition: "The redox potential of an aquarium is a measure of the aquarium water's ability to cleanse itself." Now here's the long chemistry-lesson version. You'll soon understand why we gave you the simple version first:
With the exception of energy, everything, everywhere, that's anything at all, is composed of atoms. An atom, you may recall, is composed of protons, neutrons and electrons. The protons and neutrons form the center of the atom, called the nucleus. Protons carry a positive charge, and neutrons are neutral, so the nucleus has a positive charge.
There is one negatively-charged electron for every positively-charged proton in an atom. The electrons circle the nucleus in layers or shells. It is the electrons in the outer shell that "react" with electrons in other atoms to form compounds.
The more protons an atom has, the heavier it is. Atoms with different atomic weights are known as elements. When two elements combine in a reaction, they form a compound. Compounds may exist as molecules or ions. Molecules are un-charged components of a compound. Ions are either negatively or positively-charged components of a compound. The simplest molecules are two combined atoms of one element, for example, oxygen as O2, or chlorine as Cl2.
"Redox" is short for oxidation-reduction, which is a type of chemical reaction. A redox reaction occurs when two elements combine, and one element "loses" an electron to the other element. The element that "loses" an electron is said to be "oxidized." The element that "gains" an electron is said to be "reduced." By the way, the electrons aren't really lost. They're shared in such a manner that the resulting molecule has an electrical charge. For example, when two sodium atoms (Na), and a chlorine molecule (Cl2), combine to form two molecules of table salt (2NaCl), they undergo a redox reaction. The sodium is oxidized and "loses" an electron, so that it has a positive charge. Chlorine is reduced and "gains" an electron, so it has a negative charge. The two go hand-in-hand. If one element is reduced, another must be oxidized.
Some atoms, like chlorine (Cl) and oxygen (O), really "want" to "gain" electrons. These atoms are called oxidizers. Some atoms, like sodium (Na) and Hydrogen (H), really "want" to "lose" electrons, and are called reducers. Water is an amazing molecule. It too, is formed by a redox reaction, which forms a bi-polar charged molecule, having a positive charge on the hydrogen end and a negative charge on the oxygen end, making it both an oxidizer and a reducer at the same time.
"Potential" refers to the charge of an ion created a redox reaction and dissolved in water. When table salt (NaCl) is dissolved in water, it forms two ions. One is an oxidized positively-charged sodium ion, (Na+), called a cation (+). The other is a reduced, negatively-charged ion, (Cl-), called an anion (-). The oxidation reduction potential of saltwater is the measurement of the total cations and anions in solution that are available to either oxidize or reduce other molecules. Redox potential is measured in millivolts (mV). If there were an equal amount of cations and anions dissolved in a given volume of seawater, the water would have a redox potential of 0.0 mV. Water in an aquarium has plenty of free oxygen in it (we hope!). Oxygen is a great oxidizer, and is busy "stealing" electrons, so there are always more positively-charged (oxidized) cations present in clean seawater. Therefore, saltwater in an aquarium will have a positive redox potential. The ideal redox potential in a marine aquarium is between 350.0mv and 400.0mv.
If the oxygen levels drop in an aquarium, more anions appear on the scene, and the redox potential will fall. This happens as organics accumulate in the water, reducing oxygen. If a strong oxidizer, such as ozone (O3), is introduced, the concentration of cations increase, and the redox potential will rise.
By measuring the redox potential of the water in a marine aquarium, we can tell how clean the water is. A redox potential meter only measures redox potential. A redox meter/controller not only does this, it also can be set to maintain a desired redox potential by controlling an ozonizer which doses ozone into the water, usually inside a protein skimmer or an ozone reactor. Ozone is such a powerful oxidizer, that caution should be exercised when using it. It is also used in aquariums to control un-wanted pathogenic microorganisms and parasites#
