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Using Ozone in the Home Aquarium

The use of ozone has long been a standard practice in industrial and public water purification plants, and large scale public aquarium filtration, as one of the best and most efficient means to increase water quality, while still being able to promote water conservation.   One of the biggest problems to overcome in these closed water systems is the accumulation of dissolved organic waste from various biological sources such as animal waste and decomposing food and plant material.
In aquariums of any scale, mechanical filtration will remove large organic and inorganic solids, and biological filters will remove dissolved organic material in the form of Ammonia and Nitrite, this still leaves behind a large number of other dissolved and colloidal organic materials that will accumulate over time (the ones causing colors and odors being most noticeable).  In most cases these materials are only removed by physical water changes, or chemical absorption media.  While frequent water changes may be practical for removing these dissolved materials in smaller aquariums where you are not dealing with large volumes of water, it is not a practical method for removal of these materials in large systems or in systems where water conservation is at a premium.  Using chemical absorption media is expensive, and is limited in is ability to remove all of these undesirable dissolved organics.  This is where the use of Ozone comes in, I will try to answer some basic questions about ozone below

So, what is ozone, and how does it work to remove these dissolved organic molecules?
Ozone is a naturally occurring highly reactive form of oxygen gas comprised of three oxygen molecules (O3) that is also highly unstable and short lived.  It is this inherent instability of the ozone molecule that is taken advantage of for use as a strong oxidizing agent.  “Normal” oxygen, as found in air and water, has two oxygen molecules (O2) and is very stable.  When ozone molecules break down, they lose an oxygen molecule, forming a stable “normal” oxygen molecule, and a free single oxygen atom.  It is this free oxygen atom that attaches to dissolved organic compounds, which in turn causes them to break down into simpler forms that can consumed by heterotrophic bacteria , or recombine into forms that can be removed with mechanical filtration or protein skimming.  The organic molecule that gained the free oxygen atom and subsequently broke apart is now said to be oxidized.  This is a bit of an oversimplification of the process, but it is a about as general an explanation as I can give without losing too many of you. (and myself, chemistry was never my strong point)

How do I get ozone, and how do I use it in my aquarium?

As I have already discussed ozone is a highly unstable gas, so it is not possible to store, or purchase ozone, it only has a life span of a few seconds before it breaks apart.  Ozone needs to be generated as needed with a device called an ozonizer or ozone generator.  Most modern units available for the aquarium hobby use a Corona Discharge method to create ozone. In a Corona Discharge unit, air is passed through a strong electrical field which causes atmospheric oxygen (O2) to break apart into single oxygen molecules.  Some of these oxygen molecules will then combine back together after passing through the electrical field to form Ozone (O3).  This generated ozone gas must then be quickly used before it breaks apart again.  Most marine aquarium hobbyists already have the perfect piece of equipment for introducing ozone into their aquariums, their protein skimmer.  Ozone needs to have contact time with the water so that it is exposed to the materials that you wish to oxidize.  Fractionating the ozone gas by drawing it into the air intake of your protein skimmer, you can use your skimmer as a highly efficient contact chamber.  This works for both venturi type, and air pump driven protein skimmers.  You need to make sure that your skimmer is made of ozone safe materials, and that you use ozone safe air tubing.  Some plastics and rubber can be damaged by ozone, and cause leaks or failures if exposed for prolonged periods of time.  There are also ozone reactors available, but they are a bit more difficult to use, and harder to find.

How much ozone needs to be used, and is it safe for aquarium inhabitants.

The best way to monitor and control ozone is with the use of an ORP monitor or controller.  ORP stands for Oxidation Reduction Potential, and In terms of your aquarium water, it reads an electrical voltage in Milli Volts (mV) which measures the oxidation ability of the water.  As Ozone is applied the ORP level increases.  Natural sea water has an ORP value of 350-400 mV.  ORP levels of 200 or less in your aquarium are indicative of low oxygen, high dissolved organic, conditions.  By monitoring the ORP level in your aquarium, and maintaining it between 250-350mV, you can adjust your ozone dosage accordingly. Using an ORP controller simplifies this process to shut off you ozone generated at a desired ORP level.  You should never exceed an ORP of 400mV in your aquarium.  Ozone units like the Red Sea AquaZone Plus have a built in ORP controller.

Most manufacturers of ozone units recommend a dosage rate between 5-15mg per hour per 100 liters (26 gallons) many different size units are available, so you can choose an appropriate output unit for your size aquarium, and most have a variable output.  Controlling your ozone output is very important, too much is not a good thing; very low doses will provide you with excellent results in most cases, overdosing can be harmful to both you and your aquarium inhabitants.  There are several methods to make sure that you are applying the correct amounts of ozone into your aquarium.  The goal when introducing ozone into your protein skimmer is for all of the ozone to break down in the chamber or escape through the top of the skimmer.  You do not want ozone to escape freely into your aquarium, it will also oxidize organic material in there, which will cause damage to fishes gills, and invertebrate tissue.  You also do not want high concentrations of ozone to escape into the air; it is harmfull to your lungs if in high enough levels.  Most hobbyist units do not produce dangerous levels of ozone.  You can use carbon in your sump chamber that the skimmer discharges into, or on top of your protein skimmer to absorb residual Ozone, and use an Ozone test kit to make sure that none is escaping the reaction chamber into your aquarium.  Overdosing Ozone can also produce some harmful compounds, mainly in the form of hypochloric and hypobromic acids, this is why you should not exceed and ORP of 400 mV It is a not a good idea to use ozone in small confined spaces, a well ventilated room or aquarium cabinet should be considered.  If you are not using an ORP meter or controller, a conservative approach should be used, stick to the 5mg per hour, per 100 liter rate to be safe.  Another caution when using ozone is to use an air dryer to make sure that the air that is drawn into the ozone generator is dry, a simple and effective unit like the Red Sea Air Dryer, uses regenerable desiccant  beads to draw moisture out of the air.  Moisture can react with Ozone to create nitric acid, which can damage equipment, and lower the pH in your aquarium.

What are the benefits of using ozone?


Water clarity is the number one reason most people use ozone.  There are many dissolved organics that can discolor your water, ozone will oxidize these and produce water that is crystal clear.  This is especially beneficial to reef aquariums where light penetration is crucial.  Many people do not even realize how discolored their water is until they see the difference ozone can make. Ozone also has disinfecting properties, pathogenic bacteria, single cell parasites and algae, viruses are all destroyed by contact with ozone.  Increased dissolved oxygen levels from the reduced organic load and bacterial oxygen consumption.  Ozone will destroy pesticides, detergents, and many other toxins that may be in your tap water.  Many organisms release substances that are intended to defend themselves, or inhibit predators or competitors that can accumulate over time and become problematic will be destroyed by ozone.  Ammonia and Nitrite are oxidized into less harmful Nitrate when exposed to Ozone.  And as mentioned previously, using ozone can reduce the amount of water that needs to be changed in closed systems.



I hope that this has shed some light on Ozone use in the home aquarium, and that I answered some of the questions that you may have about Ozone use.  Feel free to leave comments if you’re looking for any additional info.


Until next time,



Dissolved Oxygen

One of the most important elements of a healthy aquarium is also one of the most overlooked. Like all animals, fish and other aquarium inhabitants require oxygen to survive. Unlike air breathing animals, fish depend on dissolved oxygen in the water to “breath”. Making sure that your aquarium has proper dissolved oxygen levels is vital to the health and survival of your fish.

Many things can affect the dissolved oxygen in your aquarium. The most important things to remember are stocking levels and cleaning. Too many fish will require more oxygen than is available in the water. Fish waste, decaying food and rotting plants are all consumed by bacteria, which also require oxygen. Regular cleaning, water changes, filter maintenance and proper feeding will ensure that the bacterial demand on dissolved oxygen is under control.

There are also many things that you can do to improve dissolved oxygen in your aquarium. Most of the dissolved oxygen in your aquarium comes from the atmosphere; this is accomplished through interaction with the water surface. Increased water surface area gives your aquarium higher potential for atmospheric interaction. Turbulence and water movement along with good aquarium design will increase your aquariums water surface area, and dissolved oxygen. Use of an air pump and air stones or a power head with a venturi aeration feature will also greatly increase your dissolved oxygen. The tiny bubbles created have huge amounts of surface area and greatly increase the potential for oxygen to dissolve into the water. Temperature also plays a significant role in dissolved oxygen levels. Concentration of dissolved gas decreases with increase in temperature, so avoiding high temperatures (above 85 Fahrenheit) in very important. Taking all these factors into account when setting up an aquarium will go a long way to ensuring your long term success.

The use of ozone, especially in saltwater aquariums, can also greatly increase dissolved oxygen. Ozone is a strong oxidizer, which when properly used, will break down organic material in the water through oxidation. This greatly reduces the biological demand for oxygen, and at the same time releasing oxygen as a byproduct of the oxidation process. Ozone use is not for the beginner level aquarist and must be used safely and properly. Use of an ORP controller is highly recommended. Ozone is typically used in conjunction with a protein skimmer, or a special reaction chamber.
Until next blog,