Information and misconceptions on the functioning of ozone in a koi pond

Information and misconceptions on the functioning of ozone in a koi pond

Ozon is widely used on ponds and koi ponds. Unfortunately, there are a lot of misconceptions about ozone that are assumed to be truthful in the koi community. Various forums and koi dealers will tell you the most strange statements about ozone (which is also a reason why we don’t have that many dealers within the koi community). This is a shame, ozone is put into a bad daylight and wrong advice is given all the time. We, for example, visit koi ponds with malfunctioning ozone installations dozens of times per year.

It is high time to debunk a couple misconceptions here.

What is rest ozone?
Rest/surplus ozone and dissolved ozone are often confused with one another. Rest ozone is ozone that isn’t dissolved in water. The rising air bubbles you see in a reactor are actually rest ozone as soon as these bubbles leave the water. A rector will therefore always have a connection that the air/ozone mixture will come out of. The gas stream that exits through it contains ozone, which is called rest/surplus ozone.
This is also the reasn why we don’t like static mixers that much. A static mixer has a woefullt low efficiency which causes the most part of the mixed-in ozone to leave mixer as rest/surplus ozone. Plus, a de-gas function is often not built-in, only allowing the surplus ozone to de-gas in the pond itself !<

What is dissolved ozone?
What’s in the name… Dissolved ozone is ozone dissolved in water. Just like oxygen, ozone can be dissolved in water, even better than oxygen. A good reactor will dissolve a big part of the ozone that is mixed in. However, this is invisible for the naked eye. The amounts of dissolved ozone reached with the ozone installations on koi ponds are quite low, this has to do with the ozone concentration. This is a good thing though, for higher amounts can seriously harm your koi.
A redox value of 350~400 mV is a good value for ponds.
This value is actuelly too high for a pond, 275mV is a better directive. Strictly speaking, the correct redox value can only be determined when the pH is also known but this is a little too complicated to explain here. When the water turns blue, that’s a sign that the redox value is too high. This isn’t good for your koi, the water’s oxidation value is too high and this can cause irritation to your fish’ skin.

The pond water is blue or has a blue glow
As mentioned above, this is a sign that your redox value of your water is too high. A high redox value indicates that there isn’t a lot of material that can be oxidised in the water. The discolouration that’s possibly present is fully oxidised which causes a bright blue colour.

People sometimes claim the blue water is caused by bad contact time, they say dissolved ozone is left in the water. However, this statement is very contradicting, for when there’s a bad contact time it’s barely possible to dissolve the ozone in water, so there’s barely any in it. What they probably mean is that the water isn’t properly de-gassed (this can be caused by a contact time that’s too short) which causes ozone bubbles to be left in the water. Those end up in your pond.

A redox meter measures the amount of ozone in the water .
This is definitely not the case, a redox meter measures the oxidising capacity the water has. This indicates the extent to which the water is capable of oxidising pollution. There is a connection between the redox value and the amount of dissolved ozone at higher redox values (>500mV). But we don’t work with redox values that are that high in ponds, so in this case the redox value says nothing about the amount of dissolved ozone.
There are special meters to measure the ozone concentration in mg/l (milligrams per litre)or PPM. This is quite something else than the redox value, which is measured in mV (millivolt and not Mv, that’s megavolt!!)

Ozone makes my pond sterile.
Making a pond sterile with the recommended amounts of ozone is virtually impossible. However, free ozone (ozone bubbles, surplus ozone)can end up in your pond when used incorrectly and this has a negative impact on your fish. The effects of this can be confused with a sterile pond. The slimy skin of the koi can get irritated and in extreme cases holes may develop in their skin.

Ozone breaks down ammonia/ammonium or speeds up this process.
Strictly speaking this is true under specific conditions. At a pH higher than 7, ammonium can be oxidised (not broken down) to nitrate. However, this process takes is incredibly long. The effect of ozone on ammonium is only worth measuring at a pH higher than 9.

So, ozone will barely impact ammonium in a pond. To give you an idea: ozone can halve the ammonium concentration in 15 minutes at a pH of 9. It already takes 30 minutes at a pH of 8,4! On top of that, there’s almost always enough organic pollution in a pond for the ozone to oxidise. By the time it’s done, it’s already used up and cannot begin to work on the ammonium.
This means that, on a pond, ozone does not have effect on the oxidisation of ammonia and ammonium.

Ozone breaks down nitrite or speeds up this process.
Nitrite is converted into nitrate, without needing oxygen. The pH does not affect the conversion of nitrite, even though it’s sometimes claimed.

Ozone breaks wown nitrate and phosphate or speeds up this process.
Ozone has no direct effect on the amount of nitrate or phosphate in water.strong>

Ozone causes my biological filter to function better.
Because ozone will lower the oxygen consumption of the oxidation processes, more oxygen will be available to the biological filter. This indeed causes the biological filter to function better.

Ozone adds extra oxygen to the water.
Yes and no. The ozone that was mixed in will fall back into oxygen so there will be more oxygen in the water. But the exact same effect can be achieved with a much cheaper air pump. A big advantage however, is that ozone lowers the oxygen consumption of your pond because it oxidises substances that would otherwise need a lot of oxygen to oxidise.

Ozone helps against floating algea.
The average ozone installation on a pond won’t do a lot against algea, the reaction time is simply too short. A reaction time of 4~5 minutes is needed to kill algea. A C/T value of 1,5 is needed to properly oxidise algea, which means that, at a contact time of 5 minutes, there has to be 0.3 mg/l ozone in the water. This can’t be achieved with the average installation a pond has.

I can place a UVC lamp behind my ozone installation to break down surplus ozone.
Both surplus ozone and dissolved ozone can be broken down using a UVC. However, we strongly advise against placing the UVC lamp behind your ozone reactor. This is because UVC light causes dissolved ozone to be converted into hydrogen peroxide and OH- radicals. When you’re using a good reactor it’s not necessary to place a UVC behind your reactor to break down dissolved or surplus ozone. When you do use a UVC in your ozone installation, you should always place it parallel to or before your ozone reactor and never after it!!

You need 1 gram of ozone per 20 m³.
This depends on many fectors, the functioning of your ozone reactor and the one concentration being the most important ones. When you’re using a bad reactor, 1 gram won’t be enough, when you’re using a good one, 1 gram can be enough for 50m³ water.

1 gram of ozone, is 1 gram of ozone
This might sound a bit weird, but continue reading and you will understand what we mean by that.
It’s important to take a couple things into account when selecting an ozone generator. Because, unfortunately, most manufacturers don’t mention the measurement conditions under which the ozone yield was measured, if they even mention the ozone yield at all. So then these measurements tell us practically nothing.

The measuring conditions really matter!! The ozone yield of a lot of (budget) ozone generators is measured at a dew point of the supply air of -40 of -60 degrees Celsius (if it’s even measured at all). With a standard air dryer fed by an air pump however, you will barely reach a dew point of +5 degrees Celsius. This difference od 45 degrees Celsius does make sure that your ozone generator, in practice, won’t generate 1 gram of ozone but more likely something around 0,5 grams or less.
Besides that, the amount of air needed to produce 1 gram of ozone is also an important factor, for this determine the ozone concentration. This value says something about how easily the ozone will exchange with the water.
A good ozone generator will need between 5 and 8 litres of air to produce 1 gram of ozone per hour, at a dew pont of 0 degrees Celsius. There are ozone generators that need more than 20 litres to produce the same amount, which lowers the ozone concentration by a factor of 4!
As you can see, 1 gram of ozone isn’t always 1 gram of ozone.

Ozone is a very good and safe addition to your filter when used correctly. However, when used incorrectly, it can be dangerous to you and your fish. Please ask for advice before buying an ozone installation! Please contact us if you’re looking for more information, no strings attached.

© Tol Watertechniek