The Downsides and Risks of Using Ozonators in Reef Aquariums

Ozonators are devices used to improve water quality in reef aquariums by releasing ozone (O3) that oxidizes organic waste and eliminates harmful bacteria. While they offer benefits like crystal-clear water and pathogen reduction, ozonators can also cause significant negative effects on water chemistry and the health of reef inhabitants.

How Ozonators Work Ozonators generate ozone, which reacts with organic compounds and pollutants in water. This oxidation process breaks down waste and neutralizes bacteria. However, it also produces byproducts and triggers chemical reactions that may destabilize the aquarium’s environment.

Main Risks and Drawbacks of Ozonators

1. Lowered pH Levels When ozone interacts with water, it can create hydrogen peroxide (H2O2) and other compounds that increase the concentration of hydrogen ions (H+), which lowers the water’s pH. Lower pH levels increase water acidity, which can:

• Stress corals and sensitive reef organisms

• Slow coral growth

• Damage coral tissue and structure

2. Formation of Strong Acids Ozonators can lead to the creation of harmful acids:

• Nitric Acid (HNO3): Forms when ozone oxidizes ammonia and nitrites, lowering pH and damaging water quality.

• Sulfuric Acid (H2SO4): Can develop through reactions with dissolved sulfur compounds, further acidifying the tank. These acids can create highly acidic conditions that are dangerous for marine life.

3. Increased Silicic Acid Levels Ozone can also elevate levels of silicic acid (H4SiO4), encouraging nuisance algae blooms. Excessive silica disrupts the natural balance of reef systems and can:

• Promote diatom and algae overgrowth

• Lower oxygen levels

• Lead to ecosystem imbalance

4. Toxic Byproducts If ozone is not fully filtered or broken down, it can leave behind:

• Hydrogen Peroxide: Toxic to marine life if left in the water

• Other oxidants and unstable compounds: May irritate corals or disrupt biological processes These byproducts can cause chronic stress to corals, leading to bleaching or tissue damage.

5. Calcium Absorption Issues Low pH caused by ozone reactions interferes with calcium uptake. Corals rely on stable pH to absorb calcium and magnesium, so lowered pH can:

• Impair skeletal growth

• Weaken coral structure

• Slow recovery from damage

6. Increased Coral Toxicity Risk When the water becomes too acidic, corals are more vulnerable to toxins. Acidified conditions can damage coral tissues directly, trigger bleaching, or halt growth completely.

7. ORP and Redox Balance Disruption Ozone use raises ORP (oxidation-reduction potential), which might seem beneficial. However, ozone removes beneficial reducing agents, including hydrogen. This can:

• Lead to unstable ORP fluctuations

• Create oxidative stress in the system

• Interfere with biological filtration processes

Role of Activated Carbon To manage the chemical byproducts of ozonation, activated carbon is essential. It should be placed at the skimmer’s ozone output to:

• Trap residual hydrogen peroxide and strong acids

• Help stabilize pH by removing acidic compounds

• Prevent harmful vapors from entering the room While it helps, activated carbon cannot eliminate every trace of ozone-related chemicals.

Tips for Safe Ozone Use

• Monitor pH daily to catch sudden drops

• Limit ozone output or schedule usage to avoid over-oxidation

• Use buffering additives to stabilize alkalinity and pH

• Test for silica and implement water changes or silica-removing media

• Use activated carbon consistently to neutralize chemical residues

Conclusion While ozonators offer water clarity and microbial control, their side effects can outweigh their benefits if not carefully managed. The production of acids, toxic byproducts, reduced pH, and imbalance of key nutrients and compounds can harm your reef. Always pair ozone use with strict monitoring, carbon filtration, and pH management to protect your marine ecosystem.

Used correctly, ozonators can be helpful—but they require attention and care. For delicate reef systems, it’s often best to use them sparingly, or only when absolutely necessary.