Ozone

Ozone (O3) could be seen as an aggressive form of oxygen gas (O2). An extra oxygen atom is (forcefully) added to the oxygen molecule (O2) using a high voltage (ozone generator), creating ozone (O3). This third oxygen atom is highly reactive and seizes every opportunity to break free by bonding with any organic matter it encounters. In doing so, it oxidizes (burns, destroys) this organic matter. For example, when an ozone molecule encounters a bacterium, the bacterium is destroyed because the third oxygen atom burns it, leaving behind a regular oxygen molecule (O2).

Ozone in the pond

This combustion principle is used effectively in an ozone system for pond use. Ozone is produced in an ozone generator and then fed into an ozone reactor. This ozone reactor is usually a transparent tube in which the ozone is mixed with flowing pond water. This destroys all organic substances in the pond water, such as bacteria, single-celled organisms, dyes, and odors. The water leaving the ozone reactor and returning to the pond is therefore very clear and clean. It is important to note that no residual ozone may be returned to the pond, as this poses a risk to the fish. Ozone doesn't distinguish between good and bad and destroys all organic substances it comes into contact with, including the fish in the pond! For this reason, any residual ozone is removed from the water in the ozone reactor using carbon before it is returned to the pond.

Sterile

It's sometimes claimed that ozone sterilizes a pond, preventing fish from building up resistance to any harmful bacteria because these are simply not present due to the use of an ozone system. The fish become like greenhouse plants, which would immediately become ill in a non-ozonated pond. However, this assumption is incorrect. A RedOx meter prevents the pond from becoming too sterile.

RedOx

RedOx stands for Reduction and Oxidation. Reducing substances extract oxygen from the water (think of the rotting processes of organic pollution). Oxidizing substances increase the oxygen content in the pond, allowing oxygen-consuming processes to proceed more quickly. Using an ozone system makes the water very clean, shifting the balance toward oxidizing substances, which increases the RedOx potential. This RedOx potential is expressed and measured in millivolts. The higher the RedOx potential, the cleaner the pond. To prevent the pond from becoming too clean (sterile), the ozone generator is controlled (switched on and off) based on the measured RedOx potential (using a RedOx meter). When a certain RedOx value is reached, the RedOx meter switches the ozone generator off. When the RedOx potential drops below a certain value, the system switches back on. This allows the pond to be kept clean without becoming sterile.

Ozone, necessary?

Ozone isn't a prerequisite for successful koi keeping. It can be particularly helpful in ponds with heavy or fluctuating populations (e.g., at a koi dealer). Depending on your own situation and needs, using an ozone system is always worth considering. However, ozone is a hazardous substance that shouldn't be taken lightly. If you're considering a system, make sure you have proper equipment and are knowledgeable about its installation and maintenance.

Alternative

If a professional ozone system is too much for your pond, you can also use UVC lamps to disinfect your water. Some lamps also generate light ozone, further enhancing this effect.

Author: Joop van Tol (www.koitoday.nl)
Pictures of the ozone reactor and generator: Bas van Tol (The Ozone Specialist – Disinfection with Ozone and UV)