Ozone has been in use in reef tanks for over 30 years, but its popularity has been inconsistent. The mid-1990s saw a surge in its use, followed by another rise in 2005. The benefits of Ozone have been long debated, but it’s been consistently effective against phosphate buildup.

Ozone does not directly interact with Phosphate. Instead, it breaks down complex organics such as Oleic acid and Phenol to smaller, hydrophilic compounds such as Carbon Peroxide, which degrade faster to produce algae and bacteria. The bacteria and algae then ingest the phosphate in the tank, lowering the overall levels of toxin present.

To help you understand the impact of Ozone in reef tanks, I’ve explained how this process takes place in-depth in this article. I’ve also explained how to use Ozone and debunked some of the misconceptions surrounding Ozone use.

What Is Ozone, And How Does It Work?

Ozone is an aggressive oxidation agent that is made from 3 Oxygen atoms bonded with a 116.8° angle between 2 tail ends. This makes Ozone a polar molecule with negative charges on its 2 ends and a positive charge in the middle. Ozone has 2 resonance structures as the middle Oxygen atom keeps forming alternating double bonds with the 2 tail end Oxygen atoms. Because of this, the middle Oxygen atom is left with 2 unbonded electrons.

Due to the alternating bond formation, one tail Oxygen atom is always left without a bond, which causes Ozone to be so highly reactive and unstable. At room temperature, Ozone is an unstable gas that only lasts a few seconds within saltwater. So, Ozone must be created and supplied directly in reef tanks on the spot by splitting Oxygen molecules in the air.

At temperatures below 180° C, Ozone condenses down to a dark blue liquid with a lovely, sweet smell. It’s also the telltale sign that Ozone is forming and being injected into a reef tank.

Compared to Oxygen, Ozone is a much more aggressive oxidizing agent. Thanks to a stable diatomic bond, Oxygen does not break apart or react as easily as Ozone.

At low concentrations, Ozone can react to Iodides and produce Hypoiodate along with Hypoiodous acid. The Hypoiodous acid is a strong oxidizer, with a pKof 10.4 in freshwater. It continues reacting with other metal ions and organic compounds in saltwater, breaking them down into smaller chains.

At high concentrations, Ozone will react more aggressively and will have the necessary volume to cause a reaction with any Bromide in saltwater. The reaction forms Hypobromite, an acid with a pKof 9 in freshwater. This acid is as aggressive as Ozone and will oxidize any inorganic or organic compound it can react with. Also, it may cause a reaction with Ozone and produce Bromide once more.

Aside from these reactions, typically, Ozone will target Ammonia, Iron, and Manganese ions in saltwater. Ozone converts soluble Ferrous ions to more stable Ferric ions and creates Ferric Oxide. For both Manganese and Iron, Ozone will free their ions from strong, complex chains that are not bioavailable or biodegradable, then form Oxides.

How Does Ozone React With Phosphates?

Ozone does not interact with Phosphates directly in saltwater. Instead, Ozone’s oxidation and reduction reactions with other complex compounds within the water produce more biodegradable and bioavailable compounds that can stimulate bacteria and algae growth.

The most notable of the oxidation reactions is Ozone’s interaction with Ammonia. Ozone is very effective at converting Ammonia into Nitrate. In fact, if your reef tank has more Ammonia, then Ozone will ignore Bromate to react with it instead. The reaction will produce copious amounts of nitrate in your tank, creating an ideal environment for bacterial growth.

If Ozone reacts with Bromate in your reef tank, it produces Bromamine, which then rapidly breaks down into Bromide and Nitrate. For organic compounds such as Oleic acid and Phenol, Ozone will break the Carbon-Carbon double bonds, creating simpler compounds such as Carbon Peroxide.

Ozone will also interact with metallic ions, creating Oxides, and attack complex chains containing metals. Eventually, these biodegradable compounds will create bacteria and algae in your reef tank.

Overall, Ozone will produce a lot of organic compounds that will degrade and create bacteria and algae in your tank and create plenty of Nitrate as well. The newly grown bacteria and algae will use the produced Nitrate and any naturally occurring Nitrates and Phosphate found in your reef tank. As a result, the Phosphate levels in your tank will go down.

So, Should You Use Ozone In Your Reef Tank?

Used optimally, Ozone can be very beneficial for your reef tank. Using Ozone in reef tanks gives you these 7 benefits.

  • Increased Levels Of Bacteria And Algae Growth: Ozone breaks down complex organic compounds into biodegradable, simpler compounds. These will break down and produce beneficial algae and bacteria in your tank.
  • Decrease Toxins: Ozone will aggressively oxidize many toxic chemicals in your tank, such as Ammonia, metallic ions, complex metal chains, and Bromamine, and render them ineffective. Because it passively increases algae and bacterial growth, Nitrates, Nitrites, and Phosphate levels in your tank will decrease.
  • Improving Water Clarity: Ozone can improve water clarity by decoloring water. Ozone targets the Carbon-Carbon double bonds of naturally occurring pigments in saltwater, such as Chlorophyll, β-carotene, and Humic and Fulvic acids. By breaking these pigments, Ozone removes any yellowing effects in your reef tank water.
  • Increasing Light Penetration: Ozone removes any pigments that absorb mainly yellow and green spectrums of light and many organic and inorganic compounds that can block light. Your reef tank has a higher exposure to light and can receive all light spectrums.
  • Improve GAC Effectiveness: If you use Granular Activated Carbon with Ozone, it will have a higher rate of effectiveness. Typically, GAC can only remove up to 37% of a body of water’s TOC or Total Organic Carbon, but with Ozone, the percentage increases to 60-78. The phenomenon is caused by Ozone altering the organic molecules in a way that makes them more reactive to GAC.
  • Neutralizing Hydrophilic Compounds: Reactions with Ozone can produce smaller, hydrophilic compounds that can no longer interact with your reef tank water. In some cases, Ozone turns completely hydrophilic compounds into amphiphilic compounds. It improves your water’s quality but also makes skimming difficult.
  • Water Disinfection: Oddly enough, overexposure to Ozone can effectively kill off bacteria, algae, and other problematic growths, such as streptococci and coliforms, in your reef tank. By using around 10 ppm of Ozone for 10 minutes, you can expect 99.9% of all pests in your tanks to be eliminated.

Using Ozone also comes with some issues if you don’t prepare your reef tank for it. Ozone will oxidize components and filters in your tank, and excess Ozone escaping your tank can adversely affect your health. Ozone will also make skimming difficult, and too much Ozone can introduce Ozone Produced Oxidants or toxic OPOs in your reef tank. So, careful and planned use of Ozone is highly advised.

How Can You Use Ozone In Your Reef Tank?

To inject Ozone into your reef tank, you’ll need these components.

  • Ozone generator with ORP Controller.
  • Ozone-safe tubing.
  • Protein Skimmer with Ozone resistance.
  • Moisture absorber or desiccant.
  • Activated Carbon.
  • Media Bag.

To use this setup, follow these steps.

  • Attach the protein skimmer to your reef tank.
  • Place the activated Carbon in your media bag and place it on top of the exhaust of your protein skimmer.
  • Use Ozone-safe tubing to connect the skimmer to the Ozone generator.
  • Use the tubing to connect the generator to the desiccant.

Once you have set up your ozone generator, aim to inject as little Ozone as possible to maintain optimal water conditions in your reef tank. Start with 15 mg of Ozone per hour for every 25 gallons of reef tank water and wait a few days because, in the meantime, the ORP readings will stabilize. Do not alter the Ozone injection rate frequently or by large amounts, as this will harm your reef tank.

As for ORP or Oxidation Reduction Potential, it is an indicator of your reef tank water’s capability to break down any waste and oxidize contaminants. But higher ORP isn’t better, as this can kill off everything in your reef tank and introduce OPOs. It’s suggested to keep the ORP levels within 300-350 mV. Do not exceed 400 mV by any means, as this will create adverse conditions in your reef tank.

4 Common Myths About Ozone Usage In Reef Tanks

There are quite a few misconceptions surrounding Ozone usage in reef tanks. Some reef tank owners assume that it is the cure for everything, while many are skeptical and consider its effects nothing more than a placebo. The truth is somewhere in between, however, and I’ll be debunking 4 of the most common misconceptions from both spectrums.

More Ozone Is Better

It is a common misconception that injecting more Ozone is better. Unfortunately, Ozone at high levels can aggravate toxicity levels in your reef tank and kill off any fish or corals. High concentrations of Ozone can create high levels of Bromamine and other toxic OPOs. Above 400 mV of ORP, Ozone will create Hypobromite acid, which is an equally aggressive oxidizer and causes further damage to the ecosystem in your reef tank.

Ozone Increases Reef Tank Alkalinity

Using Ozone in your reef tank won’t increase its alkalinity. Using Ozone does not produce any COin your system, so it does not affect your reef tank’s pH levels.

Ozone Increases Skimmer Performance

Theoretically, Ozone should increase the effectiveness of a skimmer, as it can create smaller hydrophobic and amphiphilic compounds. But it breaks down compounds so much that it reduces how much your skimmer can collect.

Ozone Can Kill Your Fish And Corals

At sufficiently high levels, Ozone will kill off your fish and corals. But aquarium-level injections of Ozone are far lower than the amount needed to have the dreaded sterilizing effect. You’d need to inject more than 30 ppm over hours to cause Ozone injections to become lethal.


To easily create Ozone, you can use corona discharge Ozone generators that use electricity. For preventing rapid erosion, use Ozone-safe tubing, Kynar fittings, and Ozone-ready protein skimmers only.

And to ensure safety, always use dry activated Carbon on top of the skimmer exhaust and turn off the generator when you smell something sweet. Remember, responsible and restrained use of Ozone is the key to achieving cleaner, clearer, and safer reef tank water.

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