Ozone in marine aquarium, when does it make sense?

by | Dec 2, 2022 | Opinion, Supplements | 1 comment

Ozone (whose chemical formula is O3), is an oxygen allotropic form with a peculiar garlic smell. Its molecules, as you can understand from its formula, is made of three atoms of oxygen. So, why do we talk about it? Let’s see the pros and cons of its use in aquarium.

Let’s begin with the words of the famous marine aquariologist Anthony Rosario Calfo, who, in his Book of Coral Propagation, wrote about ozone:

The ozone excess may harm or kill every organism hosted in your aquariums. But this shouldn’t prevent you from considering its use. There are many thing that can kill or harm the organisms in the aquarium. The stupidity is the number one killer of living organisms. We can call it human mistake if it makes us fell better, but it’s still ignorance given by lack of information, unverified misinformation or failure to understand correct information.

Anthony Rosario CalfoBook of Coral Propagation – page 119

We should use this quote more often. But let’s get back to ozone.

The ozone molecule is less stable than the oxygen and tends to change into oxygen with the liberation of the ion O-. This simple transformation leads to an increase of the oxidative capacity of the system, as well as an increase of the Redox potential [or Oxidation Reduction Potential, ORP]. The increase in Redox leads to a greater capacity of the aquarium to oxidize the substances accelerating other processes, like the nitrogen cycle. Simplifying: NH3>NO2>NO3 .

Anthony Rosario Calfo during the ReefItalia gathering at Formia several years ago

After measuring the Redox potential you can adjust in order to stay under the threshold of 375-400 mV, which isn’t harmful for any organisms, human being included. Without an ozonator, you know that your aquarium is well balanced if you measure a value included between 300 and 400.

What do we need ozone for?

The first thing you will notice when you use ozone in your aquarium is that the water becomes very clear. Through the oxidation of organic compounds it bleaches and filters the water, allowing us to obtain a greater efficiency from our lights. The second thing, which is less obvious, is the decrease in the number of the more sensitive bacteria and some of the pathogens.

Then why don’t we use it every day?

Ozone has never been very popular in this hobby and industry for two reasons.

The first one is the lack of a clear perception of a real utility, granted by documented results. There isn’t enough data to link the ozone to the good maintenance of a reef aquarium, and we’re not willing to give credit to some far relative that has an incredible aquarium because he uses ozone. Then we have to consider, and Calfo said this too, that the benefits of ozone can also be obtained through other methods. For example, the use of active carbon leads to clearer water too, and if you wanted it to be even clearer you could use zeolite. To increase the oxidation we could boost the power of the LED, and so on.

The second reason is that ozone, in high concentrations, can be toxic both for the animals in the aquarium and the people living in its surroundings. That is why there’s a certain skepticism.

Ozone must always be used with active carbon, used both in water and air

The contraindications can be summed up with the formation of halogenated compounds like BrOH and BrO3– that, if not correctly removed from active carbon, can have negative repercussions on the most sensitive organisms of the the aquarium, like shrimps, small or larval fish, and even some coral.

In any case, the ionizer should be connected to an acrylic skimmer or suited for ozone administration, taking care to filter with active carbon every time you open the glass top of the skimmer, to prevent unfiltered ozone from getting into the air. Moreover, is fundamental to track the level of ORP, the Redox potential, in the aquarium, so that even if you administer ozone it wouldn’t go over 375/400 mV.

The advantages given by ozone are undeniable, but it’s also true that you could obtain the same advantages with other methods. The only application I feel sure to suggest is when you have fish-only aquariums, to prevent diseases that in reef aquariums have less chances to emerge, because off the high number of corals.

What do you think?

[Translated by Agnese Poggi]

  • danireef

    Danilo Ronchi, aka DaniReef lives in Italy where he is hydraulic engineer, but starting from his love for reef aquarium and photography, he began to write about marine aquariums from 2006 and now he's published his first book "Marine Aquarium". From 2007 Danilo writes on his blog danireef.com where publishes articles, pictures, product reviews, aquariums coverage, reportage and history of his tank. Now he's happy to be part of Reefs.com

1 Comment

  1. Don

    I used Ozone for many years. Both as a hobbyist and later on when I’m had a commercial business importing Marine Fish in the ‘60’s through ‘80’s. I used Sanders Ozonizers running through Sanders Protein Skimmers.

    At that time we never tested for ORP. NOR Mv.
    Numerous articles were written and published during that period, however it just went by the wayside and fell out of favor with most.

    I personally stopped importing and selling/using them eventually.


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