The Role of Ozone in the Aquarium or Pond

A frequently mentioned topic from aquarium and pond hobbyists is ozone. What is ozone and how does it affect the aquatic environment?

Ozone, O3, occurs naturally in the atmosphere and is formed when a molecule of oxygen, O2, is joined by a single atom of oxygen, principally from the energy derived from lightning. The ‘ozone layer’ of our atmosphere is often mentioned in the news because of the damaging effects of global industrialization on this protective ultraviolet barrier between the sun and Earth’s land surfaces. Ozone is crucial for life on Earth. Highly reactive and unstable, this water soluble gas, is a strong oxidizer with a characteristic odor.

As a strong oxidizer, ozone readily gives up one of its oxygen atoms to form bonds with other substances. At low levels, this characteristic behavior makes ozone an excellent air freshener and its solubility and oxidizing potential make it an excellent water sanitizer and antipollutant. Ozone readily sheds the extra oxygen atom, which can bind to organic and chemical pollutants making it an excellent environmental disinfectant. Its strong reactivity makes it a significantly stronger oxidizer than chlorine against pollutants, bacteria, fungi and other parasitic organisms. Ozone is relatively harmless in the environment when used responsibly.

Since ozone is relatively safe in environmental situations, it has become widely used in water purification and this application has been extended to the aquarium and water garden hobbies. Following the rapid oxidation of pathogens, bacteria, parasites and pollutants, ozone is converted back to oxygen, the offending organisms become ineffective, and no harmful by-products are left in the water to cause further problems. In aquatic systems, ozone reacts very rapidly with receptors on the outer membranes of common pathogens to disrupt their chemical and biochemical structure, rendering them ineffective as disease-causing agents.

Delivering Ozone to the Aquarium or Pond

Ozone is introduced into the aquarium or pond by means of an ozone generator. These devices, or ozonizers, generate ozone by means of a discharge lamp and are preset to deliver a measured amount of ozone to the system. Ozonizers are available in a number of sizes and features and are sold based on the number of gallons to be treated.

Ozone could result in a sterile environment. For this reason, many ozonizers are equipped with control systems that regulate the amount of ozone is introduced into the system. Ozone acts on free-swimming pathogens in aquarium and pond water. The beneficial bacteria that reduce ammonia and nitrite from fish waste and other pollutants live on the aquarium and pond surfaces and are not affected by ozone. Ozone will not harm the biological filter. There is some speculation that ozone reactions even improve oxygen availability in the tank or pond.

Measuring Ozone Levels in the Aquarium or Pond

Ozone is measured in millivolt (mv) units and is expressed as the REDOX Potential or ORP (Oxidation/Reduction Potential) of the water.

Oxidation and reduction are terms used to describe the behavior of atoms and molecules as they react with other atoms and molecules. Chemical reactions can occur by sharing electrons or by exchanging electrons. REDOX reactions proceed by exchanging electrons between atoms and molecules. A typical REDOX reaction occurs when electrons are removed from one atom (oxidation) and added to another (reduction). The movement of electrons and the tiny charges that are generated are measured in millivolts. REDOX potential is a measure of the readiness with which these kinds of reactions occur.

Sterile water, such as that used in laboratories or in medical applications, typically has a REDOX potential of around 700mv. Aquarium and pond water treated with ozone are typically maintained at 350-380mv. Ozonizers usually deliver ozone within this range. Maintaining the REDOX potential of aquarium and pond water at 350-380mv with ozone considerably increases disruption of the protective membranes of pathogens and algae with no adverse effect on fishs’ immune systems.

Ozone & Other Types of Filtration

Ozone should never be used in place of conventional filtration. Mechanical, chemical, and biological filtration are the life of an aquarium or pond. Ozone in these systems is an enhancement. Each performs a different function in the system – filtration nurtures beneficial bacteria, ozone kills pathogens. Ozone should only be used to purify water and help eliminate pathogens that can kill fish. Since UV sterilizers can handle high flow rates compared to ozonizers, it is not recommended that ozone be used in place of UV units. Even with the use of ozone and UV, disease situations can arise. When medicating a system, turn off the ozonizer and any UV sterilizers. When the treatment cycle is finished, bring them back on-line. Ozone is also safe when salt is used in the aquarium or pond as a disease preventative.

What comprises a complete ozone system?

Ozone systems are comprised of at least two components. Fully automated systems are comprised of three.

Ozone is generated with an ozone generator and must be injected into a reaction chamber. This is done best in a protein skimmer for saltwater. Air is either pushed through the ozonizer with an air pump, then through an air stone or it can be pulled through the unit by venturi injection.

A Redox controller enables the system to operate automatically and switch the Ozone supply on and off as required. A Milwaulkee ORP Controller is an excellent unit. A protein skimmer or an ozone reactor to mix the ozone produced with the water as efficiently as possible, allow it to ‘disinfect’ the water, and then remove any residual ozone before the water is returned to the pond or aquarium. Air dryers can be used, especially on smaller systems, as ozone generators produce more ozone using dry air. Buying a slightly larger ozone unit than needed is a more trouble free alternative.

Are these systems reliable?

The technology for generating and utilizing ozone has advanced considerably. Gone are the days of the bulky, inefficient, high maintenance ozone systems. The latest large systems are air-cooled and are far more efficient, producing less heat energy. The smaller systems, like the units from Sanders, CoraLife, and Red Sea, use tiny amounts of electrical energy, are simple and very reliable devices which are guaranteed. There are no moving parts in the generators and the only maintenance required is annual cleaning of the generator electrodes or electrode replacement. The protein skimmers have no moving parts, other than adjustable valves, and require little maintenance. For systems utilizing redox controllers, the redox sensor should be cleaned with a soft toothbrush once a week to prevent fouling.

Choosing the Right System

The ideal level of ozone is 0.5gm/hour and 1gm/hour for every 1000 gallons of aquarium or pond water. Select a unit that will generate the desired level of ozone for the total gallons of water to be treated. For assistance in selecting the right ozone generator for a particular system, please email us.

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