Oxygen is represented as O2, ozone is O3. So it can be seen it is oxygen with an extra! Ozone is unstable and breaks down into oxygen quickly. It can be detected by smell if it is present in enough quantity. Some retail stores use it on their seawater, usually in conjunction with protein skimmers, though UV sterilizers have superseded ozone to a large extent. It could also sometimes be used in public swimming pools and sometimes even in sewerage processing plants.

Ozone is a strong disinfectant and oxidizer. It is because of this that it has been found useful by a few aquarists in the maintenance of high quality seawater.

At the very start I would suggest that a beginner, or a novice with a few months experience, should steer clear of ozone, at least until there is enough experience to maintain quality seawater and keep livestock healthy. By this time the aquarist will no doubt have decided that there isn’t much point in using ozone! Fair enough, the use of ozone in the home aquarium is fairly rare. This is good as ozone can be very damaging if misused.

Ozone is normally used in conjunction with a protein skimmer and the first requirement is to ensure that the skimmer is ozone resistant – the information that came with the skimmer will advise this, or a phone call to the manufacturer should do the trick.

The ozone is produced by an ozonizer, or ozone generator. This works by passing oxygen through a high voltage discharge. The ozonizer will work with ordinary air but is less efficient by perhaps 50% if the air is damp. Therefore the pump supplying the air is usually connected to an air dryer. This can be a specialist piece of equipment, or a container with silica gel. The silica gel needs to be changed regularly, and the used gel regenerated.

Using a larger ozonizer in the belief that air drying won’t be needed should not be done. There is the potential for an ozone overdose which could have dire consequences.

So the ozone is passed into a protein skimmer when the efficiency of the skimmer will notably increase. This is because ozone is a strong oxidizer, more so than oxygen (O2) alone. To ensure that ozone doesn’t pass into the aquarium the seawater leaving the protein skimmer should be passed through activated carbon. The carbon should be regularly changed for new.

Aquariums using ozone should have really clean seawater with some advantages. However, there are clear dangers. If the aquarium is badly overdosed with ozone all livestock could be lost. If slightly overdosed then livestock could be adversely affected. Ozone is also dangerous to the aquarist – if ozone can be detected by smell then too much is being generated. As already said, ensure the generator cannot overdose by not buying one that is too large.

So how much ozone should be applied? The guideline is that 5 mg and no more than 10 mg should be dosed per hour for each 100 litres (circa 26.5 US gallons) of seawater in the whole system. So it is very important that the aquarist knows the net gallonage.

With an efficient and properly sized protein skimmer and a high standard of husbandry maintaining a good environment, I don’t see a reason why a home aquarist would want to employ ozone. The aquarium should be in fine condition without it.

So if I’m not a fan of ozone, why write about it? Well, I have on occasion seen new aquarists reading packaging on ozone generators and they may think that they are worthwhile if they ‘enhance’ the aquarium, particularly if the skimmer manufacturer advises that their product is ozone resistant. There are dangers that should be known.

In the correct hands ozone can be a useful tool, but for most home aquarists it is not needed and is best left alone.

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