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Ozone for Aquaculture, Koi, Fresh and Saltwater Marine Fish    
Aquaculture Titbits Saltwater and Freshwater    





See Here for Domestic Fish Tanks and Small Commercial Ozonation systems: Click Here


Ozonation Benefits:

  • Augments the performance of protein skimmers.

  • Produces transparent and healthy water

  • Diminishes the load of nitrite and ammonia

  • Augments the redoxpotential and degermination, disinfection

  • Diminishes the load of disinfectants.

  • Decomposes yellow substances (Gilvin) and enhances degradation inside the biological filter.


The Use of Ozone Improves Biological Filtration

Our experience proves that ozone treatment and biological filtration support each other very much. Hucksted already wrote about this in 1960:

 It should be discussed whether ozone treatment and biological activities of bacteria co-operate. The suspicion that by ozone treatment not only the harmful but also the useful bacteria (nitrification bacteria for instance) could be killed is quite obvious. But enough this is unfounded. Either these bacteria are not in the free water but mostly at the bottom of the aquarium or on the algae or they grow faster than they die. Probably both versions are correct. It can definitely be said that nitrification bacteria will die faster without ozone than with ozone.

What is the Adequate Dosage of Ozone?

This is a difficult question, as different circumstances in an aquarium result in different water conditions. Therefore, e.g. the fish/water relation, quality and quantity of feed, the filter system and several more criteria are very important. As a rule of thumb the capacity of the ozonizer should be calculated by .4mg per 4500 litres of water. This empirical value is the result of several years of experience. The dosage for intensive breeding stations or aquaculture systems is usually much higher. To avoid overdosing we recommend the use of a redox control meter.

Here are some guidelines:

















The Influence of Ozone on the Nitrogen Cycle

Ozone has an intensive influence on the nitrogen circuit. At pH-values of more than 7, this means that especially in salt water with a pH-value of approximately 8.2 the toxic ammonia is oxidized to nitrate (NO3). And at pH-values at around 7, like in fresh water, the toxic ammonia is not oxidized, so that bacterial oxidation is required. But in any case the very toxic nitrite step will be oxidized by ozone to nitrate - this reaction being pH-value independent - so nitrite is oxidized to nitrate in fresh water as well as in salt water. This is most important, as nitrite even in small traces is a poisonous compound for fish and invertebrates. As shown in the following diagram, the decrease of nitrite and ammonia is faster the higher the ozone content is.

Regarding the oxidation of nitrite with ozone there should be considered that ozone helps purifying aquarium water. If there should be a sudden peak in the nitrite concentration, not only the ozonizer should be switched to maximum, but also above all, the reason should be sought within the aquarium system. It might be an unnoticed perishing animal or uncontrolled decay is processing at the bottom of the aquarium. Often it is the filter which has not been cleaned for some time and which is possibly working without oxygen, i.e. under anaerobic conditions especially mechanical filters with high filtering velocity only work under aerobic conditions at first. The more solids they accumulate, the more oxygen is reduced within the filter. The aerobic biology is slowly repressed and the filter tips over to anaerobic conditions which usually results in extremely high nitrite peaks as the filter no longer reduces nitrite but on the contrary, might even produce nitrite itself. So a mechanical filter should be cleaned frequently or even better, a  biological filter should be used.

The influence of ozone on organic substances

 The general degree of pollution of water containing organic material can be measured - even if the individual chemical compounds are unknown - by the biological oxygen demand, the BOD value. The lower this value is, the better is the water quality. As shown in the diagram below, the organic load (BOD) can also be reduced by ozone. Especially organic turbidity that results in a yellow colour of the water can be reduced by ozone. Yellow substances put strain on fish!  Ozone is able to make water crystal clear.

The Influence of Ozone on Germs

A very important characteristic of ozone is its degermination action. Ozone can, even in very low concentrations, kill viruses, bacteria and other germs. It has to be pointed out, however, that within aquaria or other fish systems it can not be the aim of the ozone treatment to sterilize the water totally. This would result in a negative effect on fish and invertebrates.

Careful monitoring and adjustment of the ozone output ensures overwhelming cultures of germs are killed while avoiding total sterility. Operating this way, fish and invertebrates live in healthy and biologically active water.


The redox potential is a measured value, giving information on the reduction and oxidation characteristics of water samples. Reductive compounds decrease the oxygen content of the water. All organic compounds, e.g. proteins, faeces, feed or blood, react fast to toxic compounds like ammonia or nitrite and they start decay processes. Reductive agents decrease the redoxpotential. The water quality gets worse.

Oxidative agents are, e.g. oxygen or more intense, ozone. They are very important for any water, as of course any organism needs oxygen for its respiration but furthermore these agents are able to neutralize or to temper the negative action of the reductive compounds. As with any oxidation or reduction process electrons are released or absorbed, a voltage is caused which is measured in  mV.


Redoxpotential and Degermination, Disinfection

As already mentioned, ozone is a very good degermination or sterilisation agent, and the redox potential is an indicator of the degree of degermination. While at a redoxpotential of 200  mV 100 % germs exist, the formation of germs is reduced by increasing the redoxpotential from 200 mV to 300 mV, e.g. by 90 % to only 10 % of the formation of germs at the beginning.

If the redoxpotential is increased to a value of 400 mV only 1 % of the original germs exist. This definitely shows that redoxpotentials exceeding 400 mV are not necessary for aquarium  systems. Absolute sterility is achieved at a much higher redoxpotential of 700 mV. But this is not recommendable for aquarium-systems and can not be achieved with common aquarium ozonizers. Especially for fresh water systems with water plants or for salt water systems with invertebrates a lower redoxpotential of about 300 mV is favourable.

Redoxpotential and Algae

This special field is very difficult and each species of algae shows different reactions to ozone concerning redox changes. But it can be said that an increase of the redoxpotential supports the growth of green and higher algae and suppresses brown and red algae.

How is the Redoxpotential Measured?

All reduction and oxidation processes produce an input or output of electrons. Due to this chemical reaction in the water a voltage is produced which is measured by the redox probe; almost without using energy. During the generation of the redox tension, electrons flow from the measuring probe to the redox system (ozone - organic substances for example). As a result of  this separation of electric charges, a tension is formed on the surface of the metal sensor, which counteracts a further electron transport. A balance develops as the electro-chemical energy (voltage) and the chemical energy (oxidation or reduction energy) neutralize each other. The reference electrode forms a constant comparative or shunt potential against the metal sensor. The separation at the contact point of the electrolyte/measuring solution (water) takes place via a ceramic capillary connection, the diaphragm.


The Redoxpotential Probe (ORP) 

The redox probe consists of a glass tube with a plate of platinum or a gold pin at the lower end. At one side of the glass there is a ceramic diaphragm inserted. Inside this diaphragm there is a flow of ions in accordance with the redoxpotential of the water into the measuring chain and reverse. The electrode should remain in the water. The first time it will take approximately 30 min. before a reliable measuring value is indicated.


How to install the Redox probe?

   1.      Installation in a water stream The redox probe should be installed in a water stream or inside a tube. In calm water there is the risk that due to the poor flow around the probe wrong redox values are measured.

    2.      Avoid direct light The electrode should be installed in a dark place. Strong light can encourage the growth of algae or a layer of bacteria. Both prevent a good exchange of water in the border layer of the probe. Furthermore, the flow of ions could be reduced or interrupted. As a result the probe may memorize retarded values, and the measuring unit might show values that were measured some time ago.

     3.      Avoid soiling Soiling can lead to various impairments. Soiling of the probe usually has a reductive effect so that a too low redoxpotential can be simulated. Soiling of the metal sensor or of the diaphragm prevents the ion exchange and leads to faulty measuring results.

How to Measure the pH Value

      In any water a certain number of the water molecules are dissociated, this means that H+ and OH ions exist side by side. The pH value expresses only the activity of the hydrogen ions (the negative decadic logarithm). With a glass probe the pH value is measured by comparison of the tension between the reference electrode in a solution with a determined pH value and the measuring electrode made of glass in the water.
The characteristic of the glass probe is its especially designed glass membrane. If it contacts water it builds up a special gel-like layer, sometimes called swell layer. By the absorption of water, H+ ions are set free which can move freely in the glass membrane and in the adjoining water, thus turning the glass into an ion conductor. The glass electrode has a buffer effect filled with material at a constant pH value. This "buffer" contains the reference electrode leading off the potential. The reference electrode is made of silver and silver chloride and the inside buffer consists of a KCl solution or a KCl gel.
The silver wire coated with silver chloride reacts to the activity of chloride ions in the adjacent solution. The separation of the inside buffer and the measured water is made by a special capillary connection, the diaphragm. Contrary to the redox measurement the measuring value of the pH electrode has to be calibrated at regular intervals. This is done with two calibrating solutions as well as an adjustment screw at the measuring unit. Special care should be taken of the regular service and the operating conditions of the pH-electrode. The operating conditions are described under the heading "redox electrode"


pH Electrode Probe


The Protein Skimmer

To describe the principle or function of a protein skimmer one could simply say that air bubbles replace the filter material of a common filter system. The best protein skimmers are designed as counter current protein skimmers. The water enters the protein skimmer at the top and flows down to the bottom. The air is introduced near the bottom by wooden air stones or sucked in by an injector (Venturi) and small bubbles rise against the water stream to the top. The airflow should be sufficient enough to fill the cross-area of the protein skimmer.
When designing our protein skimmers, great attention was paid to obtain a relatively large volume to get nearly laminar flow conditions. This is very important for the contacting of the air bubbles to the protein compound as well as to the waste particles. High turbulence in a protein skimmer may look nice but they result in a break off of the contact between the air bubbles, protein compounds and waste particles and will consequently reduce the foam efficiency remarkably. When the air bubbles have passed the reaction tube of the protein skimmer they reach the water level and together with waste particles and proteins they form viscous foam in which proteins link the air bubbles and the waste particles.        

 The following reaction can be described:

      1.      Undissolved surface-active solids can be deposited on the interface between water and air and thus be concentrated in the foam.

      2.      Undissolved, non surface-active solids can contact dissolved surface active compounds, and then be concentrated in the foam.

      3.      Dissolved waste material can partially be oxidized by ozone, so that the rising air bubbles can contact them.

The waste foam built up in this way will be transported by the upward streaming airflow via the foam tube into a foam beaker. On the way through the foam tube the foam is drained so that excessive water flows back into the protein skimmer and the water loss is minimized. The foam itself becomes concentrated. At the end of the foam tube the foam should "grow" slowly and relatively dry out of the foam tube and fall down into the foambeaker

How to Clean the Foam Cup

The common protein skimmers have a foam cup that can be removed easily and cleaned under the tap. Furthermore at some skimmers it is possible to connect a tube for draining off the waste foam. Some skimmers have a special water rinsing ring nozzle that washes off the foam continually.

What are the Main Advantages of a Protein Skimmer Compared to a Mechanical Filter?

  • The protein skimmer removes protein compounds and other organic substances before they are decomposed to toxic substances.

  • Waste and toxic substances that have been foamed into the foam beaker are totally separated from the aquarium water and its circuit!

  • Water that has passed the protein skimmer is purified of waste and furthermore highly enriched with oxygen, which is essential for aquatic life!

Which Kind of Aquaria Can Be Equipped With a Protein Skimmer?

Protein skimmers most efficiently used in salt-water aquaria - the bubble size is much smaller and effective. The diagram below shows that already at a salt concentration of only 10 per mil bubble diameters of less than 1 mm are found. This is of importance as the smaller the air bubbles the better the contacting of the bubbles to waste particles. So protein skimmers do not only work in water with a high salt concentration, as the Red Sea or Pacific water with 35 per mil and more, but also in water of the eastern seas with only 15 per mil. Indeed, a protein skimmer are not as effectively used in fresh water, as the air bubbles in  fresh water with approximately 4 - 5 mm in diameter are too large for protein skimming (salt is often added to aquaculture/Koi ponds) which assists with this problem. In salt water there are good results for quite different species of animals. So protein skimmers are used successfully for invertebrates and crustacea as well as for fish, for ornamental fish as well as fish for food, in the home aquarium as well as in public aquaria.

Here's a medium sized system ozone dosing off oxygen with contacting system and offgas destruct.














Here's slightly larger contactor in sketch showing ozone flow through the system

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