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Ozone for koi ponds

Information about ozone used for koi ponds

Ozone is widely used on ponds and koi ponds, unfortunately wide-spread knowledge about ozone in the koi community is often incorrect. On the various forums and at countless koi dealers you will come across the wildest statements about ozone (partly because of this we have got a very limited number of dealers in the koi world). This is unfortunate, it puts ozone in a bad light and leads to bad advice. Each year we visit dozens of ozone systems on koi ponds who doesn’t function properly.

It’s time to clear up some stubborn misunderstandings here.

What is residual ozone.
Residual ozone and dissolved ozone often get mixed up. Residual ozone is ozone that is not dissolved in water. The air bubbles that can be seen rising to the surface in a reactor is therefore actually residual ozone as soon as these bubbles leave the water. A reactor will therefore always have a connection from which the introduced air/ozone mixture exits. The gas stream contains ozone, or, in other words, residual ozone.
This is also one reason why we are against static mixers. In most cases there is no way for the water to degas before it enters the pond, so all residual ozone will degas in the pond itself!

What is dissolved ozone.
The name says it all, ozone that is dissolved in water. Like oxygen, ozone can also be dissolved in water, even better than oxygen. A good reactor will therefore dissolve a large part of the ozone introduced in water, which cannot be seen. With the installations that are used on koi ponds, only very low values ​​of dissolved ozone can be achieved, this has to do with the ozone gas concentration. This is a good thing because higher values ​​can be bad for your koi.

A ORP/redox value of 350~400 mV is a good value for ponds.
This value is actually too high for a pond, 275mV is a better guideline. Strictly speaking, the correct ORP/redox value can only be determined if the pH value of the water is also known, but this goes too far to describe here. A ORP/redox value that is too high can be recognized by the blue coloring of the water. This is not good for the koi because the oxidation value of the water is too high, this irritates the mucous membrane of the koi.

The pond water is blue or has a blue glow.
As mentioned above, this is a sign that the ORP/redox value of the water is too high. A high ORP/redox value indicates that there is little material to be oxidized in the water. Any discoloration present in the water is completely oxidized, giving the water a clear blue color.
It is sometimes claimed that blue water is due to a bad contact time, so dissolved ozone would remain in the water. However, this statement clashes; After all, with a bad contact time it is hardly possible to dissolve ozone in water, so there is hardly any dissolved ozone in the water. What is probably meant is that the water is not degassed properly (which may be caused by too short contact time), so that ozone bubbles remain in the water. These bubbles then end up in the pond.

A ORP/redox meter measures the amount of ozone in the water.
This is certainly not the case, a ORP/redox meter measures the oxidizing capacity of water. This gives an indication of the extent to which the water is able to oxidize pollution. At higher ORP/redox values ​​(>500mV) there is a reasonably clear relationship between the ORP/redox value and the amount of dissolved ozone. Since we do not work with these high ORP/redox values ​​in ponds, the ORP/redox value in this case says nothing about the amount of dissolved ozone.
If you want to measure the amount of dissolved ozone, there are special meters available that indicate an ozone concentration in mg/l or PPM.

Ozone makes my pond sterile.
Making a pond sterile with the amounts of ozone that are usually advised is virtually impossible. If used incorrectly, free ozone can enter the pond water (the aforementioned ozone bubbles / residual ozone) which has adverse consequences for your fish. The consequences of this can however be confused with a sterile pond. This irritates the mucous membrane of the koi and in extreme cases, holes can even appear in the skin.

Ozone breaks down ammonia/ammonium or accelerates this process.
Strictly speaking, this is true under certain circumstances. At a pH higher than 7, ammonium can be oxidized (it does not break down) to nitrate. However, this process takes a very long time. The influence of ozone on ammonium is only significant at a pH greater than 9.
In a pond, ozone will therefore hardly affect ammonium. To give you an idea, at a pH of 9, ozone can halve the ammonium concentration in 15 minutes. At a pH of 8.4 this takes longer than 30 minutes! In addition, there is usually so much organic pollution in ponds to oxidize that the ozone has already been used before it can do anything with ammonium at all. For a pond we can therefore safely say that ozone has no influence on the oxidation of ammonia and ammonium.

Ozone breaks down nitrite or speeds up this process.
Nitrite is converted to nitrate by ozone, without the need for oxygen. Although it is sometimes claimed by others, the pH does not affect the conversion of nitrite.

Ozone breaks down nitrate and phosphate or accelerates this process.
Ozone has no direct effect on the nitrate or phosphate content in the water.

Ozone ensures that my biological filter will function better.
Ozone oxidizes organic matter which results in a lower oxygen consumption. So because of this, more oxygen is available for the biological filter. This will allow the biological filter to function better.

Ozone adds extra oxygen to the water.
Yes and no. The ozone introduced will fall back to oxygen and thus increase oxygen levels. However, the same effect can be achieved much cheaper with an air pump. What is an important advantage is that ozone will reduce the oxygen consumption of your pond because it oxidizes substances, which would otherwise require a lot of oxygen.

Ozone helps against algae.
The average ozone installation on a pond will do little against algae, the reaction time is simply too short. A minimum reaction time of 4~5 minutes is required to kill algae. A C/T value of 1.5 is required to properly oxidize algae, with a contact time of 5 minutes this means that there must be 0.3mg/l ozone in the water, which will not work with an average installation on a pond.

I can place a UVC lamp behind my ozone installation to break down residual ozone.
Both residual ozone and dissolved ozone can be broken down with UVC. However, we strongly advise installing a UVC lamp infront of or parralel to the ozone reactor. Installing a UVC behind the ozone reactor can cause the formation of hydrogen peroxide and OH radicals. If you use a good ozone reactor, it is not necessary to use a UVC lamp to break down dissolved ozone or residual ozone. 

1 gram of ozone per 20 m³ of water is required.
This depends on many factors, the efficiency of your ozone reactor and the ozone concentration are the most important of these. With a bad ozone reactor 1 gram of ozone will not be enough, with a good ozone reactor 1 gram can be enough for 50m³ of water.

1 gram of ozone is 1 gram of ozone.
This might sounds a bit strange, but after reading the text below, you will understand what we mean by this. When looking at the numbers about ozone generators, it is important to understand the context behind them and to ask yourself wether or not these numers are true. Is 1 gram of ozone really 1 gram? For example, under what circumstances was the measurement performed, and was it measured at all?

Unfortunately, most manufacturers do not state the measurement conditions under which the ozone yield is measured, so in fact this value means nothing. However, the measurement conditions make a big difference! The ozone yield of many (budget) ozone generators has been measured at a dew point of the supply air of -40 or -60 degrees (if this has been measured at all). With a standard air dryer fed by an air pump you will hardly reach a dew point of +5 degrees. However, this 45-degree difference means that your ozone generator does not produce 1 gram of ozone, but probably 0.5 gram or less.

In addition, the amount of air needed to make 1 gram of ozone is an important factor, as it determines the ozone concentration. This value says something about how easily ozone will dissolve into the water. A good ozone generator will need between 5 and 8 liters of air (dew point of 0 degrees) to generate 1 gram of ozone per hour. There are also generators that need more than 20 liters for the same amount of ozone, the ozone concentration is then a factor of 4 lower! As you can see, 1 gram of ozone is not always 1 gram of ozone. F

The following Dutch article holds more information about the ozone concentration and its influence on the dew point of air. Ozon zo zit dat dus (LET OP bestand is 9Mb!)

Ozone is a very good and safe addition to your filter when used correctly. However, if used incorrectly, it is dangerous (both for you and for your fish), so be sure to gather enough informtion and advice before purchasing an ozone installation! Please feel free to contact us for more information.

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