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Q10541 - INFO: The Use of Ozone in the Marine and Reef Aquarium by Paul Besant, Red Sea Tech Research Dept
Aquarium filtration systems have improved greatly during the last ten years and the desire to achieve the best water quality encourages today’s fish-keepers to use high flow mechanicaL /
biological filters, large foam fractioners (Protein skimmers), U.V. sterilizers and more. However even with the quality of today’s aquarium filtration, there are a few dissolved and fine organics components that tend to accumulate in an aquarium which the ordinary filtration systems fail to remove. Generally the only way to reduce them is by frequent water changes.

Conventional means of solids removal, such as sponge/ perlon floss filters and sand filters address the removal of coarse settleable and filterable solids, but not the removal of fine colloidal solids. Similarly, nitrifying bacteria in bio-filters remove dissolved ammonia and nitrite, but not all dissolved organic wastes. As an aquarium matures, the accumulation of dissolved organic colloidal solids increases. This organic buildup decreases the performance of the nitrifying bacteria that convert nitrite to nitrate, thus causing harming nitrite buildup. The biochemical oxygen demand also rises, so the oxygen levels decrease over time. These shifts in water parameters stress the aquarium inhabitants and may even cause mortality. To reduce the necessity of large water changes, that can change the systems chemical parameters (PH, salinity, alkalinity etc.), there is a very efficient alternative method of breaking down these organic wastes using a strong oxidizing agent, this method is “Ozonation”.

Ozone (O3) has been used, for a long time as a disinfectant and as an oxidizer that removes turbidity, algae, odor, color and taste in the municipal drinking water supply. Applying ozone to fresh water, marine and reef aquariums will achieve the following properties:
  • Removal of Micronics solids (1-100 microns) by clumping them together to bigger dimension particles that can be removed by the protein skimmer or activated carbon.
  • Removal of complicated dissolved organics that cannot be handled by ordinary bio-filter. The ozone oxidizes them and breaks them to simple organics that are now available for degradation by heterotrophic bacteria.
  • Reduction of harmful ammonia (NH3-) and nitrite (NO2-) levels by oxidizing them to nitrate (NO3-).
  • Precipitation of metals, such as aluminum.
  • Algae control
  • Destruction of harmful inorganic components, such as sulfides.
  • Degradation of pesticides and detergents.
  • Bacterial disinfections & viral inactivation: 0.4 mg/L at a 4-minute contact time easily kill bacteria and inactivate 99% of viruses.
Ozone is a very unstable molecule that is formed when an Oxygen molecule (O2) bonds to a third oxygen atom by passing the oxygen through an electrical charge or U.V. light at the proper wavelength. Because of the loosely bound third atom, ozone exhibits a far greater oxidative potential compared to oxygen. The ozone reacts with organic molecules at unsaturated carbon bonds, which quickly decompose in water to form carbonyl components and hydrogen peroxide. In solution ozone has been shown taking to pathways as it decomposes and oxidizes materials. The first pathway is by direct reaction with molecular ozone and the second is by indirect action of the oxidized compound with radicals formed by the decomposition of ozone.

The advantages of ozone are:
  • Powerful oxidizing agent. Reduces BOD and COD levels.
  • Very rapid reaction time.
  • 5 times more effective as a disinfectant for bacteria and viruses, than Cl2.
  • Requires short contact time.
  • Produces a complete reaction because of its short half-life (20-30 min.)
  • Leaves a beneficial oxygen residual
Production and utilization of ozone:

As ozone is applied to aquarium water it will raise the oxygen level and break down organic wastes, i.e. sterilizing the water thus raising the redox potential. Most commercially available ozone generators use corona discharge to establish a strong electric field. Dried air or oxygen gas is fed through the electric field. Due to the electrical energy, a proportion of the oxygen molecules become excited, creating oxygen atoms that bind to other molecules to create ozone.

The feed gas must be dry and free from impurities. If a feed gas of air or low purity oxygen contains moisture, nitric acid is formed, which rapidly decomposes the produced ozone and is also highly corrosive.

The design of the ozone-to-water contact chamber is the most critical design element in using an ozone system. Since ozone in the carrier gas (air) is at relatively low concentration, mass transfer of the ozone from a gas into the water must be done at maximum efficiency. In marine and reef aquariums, we already have an efficient reactor vessel in which to utilize ozone, our protein skimmer. The protein skimmer materials must be highly resistant or inert to ozone. Use of improper materials can lead to erosion of the unit and cause leakage.

Ozone can be applied continuously, as a series of treatments, or as single batch treatment per day. The optimum rate for disinfection is highly variable and represents the sum of ozone demand from dissolved organics, colloidal solids, etc. The amount of ozone necessary is largely dependent on the background organic loading of the water to be treated. In pure water, residual concentration of 0.01-0.1 ppm for period of 15 seconds can be effective in reducing bacterial loads. In most of our aquarium systems 5-15 mg/hr/100 liters is sufficient amount to get proper disinfection. A more accurate rule is 1.5 mg for 1hr/day/ 1 gr of fish weight. If the purpose of the ozone is to treat the dissolved organic matter, the optimum rate should be according to daily feed rate. It is recommended 10 mg ozone per gram of fish food, to reduce accumulated organics.

The best method to monitor ozone input is by measuring the oxidation-reduction potential (ORP) with probes or by a Redox meter/controller. The term Redox potential refers to the electrons transfer from one substance to another that takes place in every chemical reaction. The substance that receives electrons is said to have been oxidized, while the one that loses electrons is said to have been reduced. In sea water, many of these so called ‘redox reactions’ occur simultaneously. Because of the constant exchange of electrons the amount of prevailing oxidative or reductive reaction can be measured as a voltage, by means of a platinum electrode and a volt meter. The higher the redox potential, the greater the oxidizing capacity of the water. In sea water the redox potential is between 350-400 mV. Redox potential values of between 300 and 350 mV are recommended as the desirable level, which indicate an oxygen rich environment with low dissolved organics. The redox potential can therefore be used as an indication of the quality of your Aquarium environment. Values below 200 mV indicate an accumulation of disolved organics and a low oxygen level.

As ozone is applied to aquarium water it will raise the oxygen level and break down organic wastes, i.e. sterilizing the water thus raising the redox potential. A too high redox potential is as undesirable as a low redox potential therefore it is advisable to keep the redox potential stable by aplying ozone. When the redox potential is lower than the desired value, ozone should be applied and when the upper limit of the redox potential is reached the ozone should be turned off. This control can be achieved by combining a Redox controller to the ozone generator.

Red Sea manufactures a range of technically advanced ozonizers (The AquaZone) with 50, 100 and 200 mg/hr output. Red Sea also offers AquaZone PLUS which combines an Ozonizer and Redox controller. The following chart will help to determine the ozonizer suitable for each kind of system up to the maximum volume indicated.

Ozone Output Freshwater Tank/
Indoor ponds
Outdoor Ponds Freshwater
Marine Tank Reef Tank Marine Quarantine
Marine Hatcheries
50mg/hr 500 L /
132 gal
300 L /
79 gal
1000 L /
264 gal
500 L /
132 gal
1000 L /
264 gal
300 L /
79 gal
500 L /
100mg/hr 1000 L /
264 gal
600 L /
158 gal
2000 L /
528 gal
100 L /
264 gal
2000 L /
528 gal
600 L /
158 gal
1000 L /
264 gal
200mg/hr 2000 L /
528 gal
1200 L /
317 gal
4000 L /
1056 gal
2000 L /
528 gal
4000 L /
1056 gal
1200 L /
317 gal
2000 L /
528 gal

Safety Precautions for using Ozone:

Ozonized air should be prevented from escaping into the room; it is advisable to install a carbon filter on your protein skimmer or ozone reactor where ozonized air escapes. Do not let the redox value of the aquarium water exceed 400 mV as harmful substances (commonly in the form of hypochloric and hypobromic acids) can be produced, which could damage sensitive organisms. The aquarium inhabitants should be protected from exposure to free ozone and /or oxidation products. The recommended method to remove any residual free ozone and any free oxidation products is by vigorous aeration followed by filtration through activated carbon. After this treatment the amount of residual ozone should be checked regularly – maximum 0.05mg per liter. (Testing residuals can be achieved by using Red Sea’s Residual Ozone Mini-Lab Test).
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Approved Comments...
I needed to know the amount of ozone to be applied to my saltwater fish only tank. The angel fish has hole in the head disease and activated carbon has been completely removed. I have Red Sea protein skimmer with Aqua Zone Ozonizer which employs with ORP controller. UV light is also being used periodically to control the hardness of the water for sensitive Angels and yellow tang. Literal line disease is likely to be caused by activated carbon and since activated carbon was removed, it has started to reverse very slowly. Although to keep the water quality Ozone has to be applied, but too much of Ozone will kill the fish. Redox Potential is set by 350. Approved: 1/6/2014
very informative information. Thanks to the writter Approved: 7/6/2013
many aquarium keepers spend more money on chemical filtration and lighting because they know little about ozone. This article should give a better understanding and reason to use it. many pro aquariums use it, why shouldnt hobbiests use it too? Approved: 7/4/2013
very good infomation Approved: 1/5/2013
I use ozone 24/7 and still found this article easy to read and very useful Approved: 7/2/2012
It is a complete and extensive narrative of all the pros and cons of an ozoniser . Approved: 11/8/2011
Great article I am using ozone for three years and controlling by ORP and now everything makes sence! Approved: 8/18/2011
enjoyable read Approved: 7/14/2011
This article provides excellent interpretation for both the scientific aquarist and the layman and/or beginner. Very well laid out, and offers a variety of points from benefits, use, effectiveness, and science behind of ozone use in the aquarium. I enjoyed reading this article very much. Brian Schlindwein Approved: 12/6/2010
Because I get all what I want to know about the ozonizer Thanks for the writer Approved: 12/15/2009
I have read this article and others about ozone generators and aquariums. Some other articles (perhaps more frank) also mention that ozone should not be introduced directly to the water in the aquarium. One article refers to the equipment sold by Red Sea as excellent but there is a specific means by which ozone should be used to sterilize the water in the tank. Approved: 11/11/2009
Great article, the only concern that I had was in trying to understand how a Ozonizer that is controled by a Redox probe that is set to control the system at a value of 360mv +/- 10mv could reach a redox level of 415mv. If this level is high, is there any way of reducing these toxic levels. Approved: 4/2/2008
well written, clear,covers the topic completely, short. Approved: 2/14/2008
Hydrogen Peroxide (H2O2) is a liquid and cannot be seperated from you tank water as ozone, a gas can be. You dont want to cxidize your fish! Also when H2O2 losses its oxygen it turns to water which in heavy doses can lower salinity. Approved: 2/9/2008
Because for the first time in over 25 years, Ive seen ozone explained properly. George Goulart, Jr. owner Aqua-Life Aquarium. Established 1976 Approved: 2/9/2008
I have an ozonizer and a protein skimmer to introduce ozone into the water but I have never used it because I was not comfortable with my knowledge of ozone usage. I also have an ORP probe connected to my Aqua Controller that reads ORP. This article really cleared up some things for me and I feel more comfortable to at least gradually start to use ozone and see what the results are in my aquarium. Approved: 2/9/2008
The article seems thorough however without outside sources I cannot be sure the article is complete nor accurate in all regards. I rate it 8 of 10. Approved: 2/9/2008
This article contains a lot of incorrect information. There is also a lot of highly questionable information in the article. I can not help but believe that this was produced only as a fast talking sales pitch for ozone and Red Sea Ozonizers, and their related products. Yes, ozone does have its uses in many aquarium areas. However, by sending out an article of such low quality, you are doing yourself and the hobby a great disservice. Approved: 2/9/2008
It was informative Approved: 2/9/2008
This is very good article. The knowlegede base provided is great. It is not clear, if the final product in the water is hydrogen peroxide, why H2O2 can not be used instead Ozone, which more economical. Approved: 2/9/2008
Article Details
Created on 2/6/2008.
Last Modified on 12/10/2008.
Last Modified by Keith MacNeil.
Article has been viewed 24413 times.
Rated 8 out of 10 based on 116 votes.
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