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Ozone for Reef Tanks
Last updated on March 14th, 2025
What is Ozone Filtration for Reef Tanks
Ozone has been a topic over the last couple years as a filtration method for reef tanks. Ozone's use for reef tanks is very similar to that of UV where it gets rid of that yellow color and makes your water crystal clear. This Ozone filtration works by adding a volitile O3 molecule to the water. This has the ability to limit bacteria, toxins, and affecting other parasites.
How Does Ozone Work?
First, you need to use an Ozone Generator. This uses a high voltage discharge to seperate Oxygen atoms which then rejoin to become O3, or Ozone. Ideally, you should also have an air dryer before the Ozone generator. Drier air produces more Ozone, and can reduce the amount of nitrogen added to the aquarium. After this, the Ozone is mixed with the aquarium water. Typically this is done in a protein skimmer to maximize contact with the water.
While in the protein skimmer, or other reaction chamber, the ozone breaks down into Oxygen, O2, and the extra oxygen ion then "oxydizes" the water. This is what removes parasites, bacteria, toxins, etc. Whatever is used to mix the ozone with the water should then run the outlet water over carbon. This removes extra oxygen and some of the oxidized toxins and other organic compounds. You should also have carbon where the air leaves the protein skimmer. This is to protect you and your family from any ozone that may exit the skimmer in the air.
Borrowing this image from
Risks of Ozone
I think we covered most of the reasons why you may want to use ozone and how it works. Here are a few risks to consider though.
Off the bat, you will want to be sure that excess ozone doesn't leave the aquarium. Ozone can be bad for your lungs and overall health. In general, you'll know by the smell. Ozone smells like a thunderstorm right after lightning strikes. Specific, I know...
You must also use ozone safe tubing and plastics, such as the protein skimmer, because ozone causes plastics to break down and become very brittle. This is also why you want carbon on the water output from the reaction chamber. The ozone can cause the seals for your tank to become brittle.
Ozone Setup Specifics
When setting up ozone, first you need to know how you're adding the ozone to the water. If it is using the air intake pump from a protein skimmer, you shouldn't need to add anything special. If not though, you may need to add an air pump to push the air through the ozone generator and into the reaction chamber.
As for the Ozone settings, you will want between 0.3-0.5 mg of ozone for every gallon. You can change this over time, but you will want to target and ORP of about 350. Which brings up the next detail, if the ozone generator doesn't use an ORP probe, you will want a controller that does use ORP and can turn the ozone generator off.
Next, you'll want an ozone resistant check valve, and to mount the ozone generator above water level. This prevents a back-siphon if anything goes wrong. This would both damage the equipment and flood your home.
You will want to replace activated carbon and reactivate/replace dryer media frequently to maintain efficiency. The wet carbon needs to be relaced every 2 or 3 days, and the dry carbon is tough to say, but likely weekly. The air drying media is typically color changing and will indicate when it needs to be changed.
Conclusion
In summary, Ozone can be used to make your reef tank look crystal clear, and even remove bacteria, toxins, and algae production. However, there is a resonable price tag and regular maintenance. There are risks to using ozone, which is largely why I don't currently utilize it. While a large amount of the benefits overlap with the safer UV option, the toxin removal seems like a great benefit for those with multiple types of anemones or coral that utilize toxins.
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About the Author
John Krenzer
John is a Software Engineer with a passion for saltwater aquariums, as well as the founder and president of Reef Stable. He started in the aquarium hobby as a child with a 20 gallon freshwater aquarium. His interest in aquarium life grew and in 2008, John set up his first saltwater aquarium.
Today, John maintains an over 300 gallon reef tank system, consisting of a 120g reef and a 210g reef. These large tanks are contained within the same system, sharing a sump as a means to reduce total maintenance and increase total water volume.
John writes articles for the blog as a means to learn about more reef aquarium topics. These articles act as a reference for the readers as well as himself. John updates these articles frequently to provide additional information or make corrections as new information becomes available.
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