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1. Introduction to Ozone & Redox Potential
1.1 What is Ozone?
Through an electrical discharge in air, three oxygen molecules can combine to
form two ozone (O3) molecules. In nature this happens for example in a
thunderstorm by the action of lightning. Ozone can be made artificially on a
small scale through electrical discharges inside an ozone generator. Ozone is a
very unstable combination, which will be oxidized by this reaction. Ozone is
therefore a very strong oxidizer.
1.2 What can Ozone do for the Aquarium?
Due to its oxidizing capabilities, ozone can break down harmful waste products
produced by fish. In a marine aquarium (or in a freshwater tank with pH higher
than 7.5), ammonia is efficiently oxidized to less harmful nitrite and further to
nitrate. This oxidation reaction can also be performed by bacteria in a biological
filter, however it is advantageous to install an ozonizer as a backup to prevent
dangerously high ammonia levels. This backup function is especially important
in aquaria with a lot of fish and subsequently a lot of waste.
More complex organic wastes, such as the substances that turn the water yellow,
cannot be removed by biological or mechanical filtration. Ozone however, breaks
up their structure, so that the fragments can be cleared up by the filter’s
bacteria or through protein skimming. The use of Ozone leads to “Crystal clear”
water.
Another important property of Ozone is its sterilizing ability. Harmful bacteria
and other possible pathogens that float in the water are efficiently killed by
ozone. In the sea the amount of floating bacteria is always very low, due to the
antiseptic action of natural sea water. In the aquarium however, bacteria that
can be harmful to many aquarium inhabitants, especially fish larvae, find a
favorable environment for rapid reproduction. The term “sterilizing” should not
be taken too literally. The amount of ozone administered should be just enough
to kill only surplus bacteria. Totally sterile water is just as harmful, to fish and
invertebrates.
Ozone should never be introduced directly to the aquarium water: it must be
administered through an isolated chamber like a pressurized ozone reactor or
a protein skimmer. A freshwater aquarium can be ozonized by connecting the
ozonizer to an air-driven internal filter.
1.3 How much Ozone should be used?
The ideal dosage will vary for each aquarium. The right dosage of ozone is
dependent on a number of factors: the volume of water, the water flow rate,
the ozonized air flow rate, the amount of dissolved organic matter, the fish
density, the type of biological filtration and additional equipment in use. As a
guideline, the ozone production should be between 5 and 15 mg/hr per 25
gallon (100 liter) of aquarium water.
Aquaria densely populated with fish need more ozone input than invertebrate
tanks where far less waste products are produced. Small reef aquaria (few fish,
many invertebrates) can be successfully maintained with less than 5 mg\hr\25
gallon. Dosages in excess of 15 mg\hr\25 gallon, should be used with extreme
caution and only, for example, in a tank densely populated with fish and no
invertebrates.