Ozonizers for aquariums.
There are two methods of generating ozone for use in aquariums. In the first case, ozone is formed from atmospheric oxygen via a photochemical reaction caused by short-wave ultraviolet radiation, and in the second case, through a corona discharge taking place in a special sealed discharge tube. Ozone is produced in special devices called ozonizers.
There are special aquarium ozonizers, such as “Coralife-25”, higher-capacity “Coralife-50” and “Coralife-100”. There are also more expensive models. Ozonizers come in various sizes rated for 10 – 1000 mg of ozone. It is important that replacement parts are easily accessible for them. The safest way to produce ozone is a household ozonizer with a capacity of 10-50 mg of ozone per hour.
DIY ozonizers powered by a 220 V and 50 Hz mains can be assembled even by a beginner in electronics. When designing and manufacturing items that contain ozone, it should be taken into account that ozone and its aqueous solutions are extremely aggressive and destroy steel, cast iron, copper, rubber, and ebonite. An ozonizer can only be made of anticorrosive materials such as stainless steel and polymers; the device can be insulated using synthetic silicones or epoxy adhesives. Among metals, stainless steel and aluminum should be used, as they can last for several years. Connecting tubes are made of polyvinyl chloride and similar materials, and seals are made of ethylene propylene. Ceramics and glass are resistant to ozone.
The air pump (micro-compressor) must be installed before the ozonizer. It should force air into the discharge tube rather than suction it through itself, otherwise the ozonized air will quickly destroy the rubber parts of the pump. The rubber diaphragm, for example, fails after just a few minutes of operation. For the same reason, rubber connecting hoses must not be used; they must be replaced with PVC tubing.
To avoid reducing the efficiency of the ozonizer, dry air must be supplied to it. Ozonizers are used with a special air-drying filter filled with small silica gel beads or calcium chloride, which absorb moisture from the air, allowing dry air to enter the ozonizer. This increases the efficiency of the ozonizer by 3-4 times. Regular airstones must not be used during water ozonation. Airstones must be made of plastic, and air ducts of polyethylene. Metal parts must not be used under any circumstances, as they will react with ozone.
Aquarium water treatment with ozone is carried out in special contactors. Water ozonation should be carried out not in the aquarium itself, but in a separate vessel to avoid harming the fish. It is important that the contactor is sealed so that ozone does not escape into the room. Even in small amounts (0.1 mg/m3), ozone causes headaches, and at higher concentrations, nosebleeds.
It is essential to remember that if you smell ozone in a living room with an aquarium, its concentration is too high and harmful to health. The apartment should be ventilated, the ozonizer turned off, and all connecting tubes thoroughly checked, along with the residual ozone absorption system using activated carbon.
It should not be forgotten that due to its unique oxidizing capacity, ozone causes accelerated degradation of all plastic tubes, connections, and other elements in contact with it. Therefore, all ozone plumbing should be regularly inspected, and upon detecting cracks or a significant decrease in hose elasticity, they should be replaced with new ones in a timely manner. It is recommended to ozonate water before pouring it into an established aquarium, while the water of an established aquarium is best passed through and with the help of a simple external filter so that air bubbles with ozone do not come into contact with fish and plants, and only ready ozonized water reaches them.
Water from this vessel should be fed into the aquarium through a carbon filter, which removes traces of dissolved ozone, preventing them from reaching the fish. Even ozonized water filtered through activated carbon retains its bactericidal properties almost entirely. In addition, the ozone dissolved in the water will continuously regenerate the carbon. The lifespan of activated carbon when filtering ozonized water is significantly increased compared to other methods of using it for aquarium water purification. This happens because ozone cleans its pores, which normally quickly become overgrown with organic matter. Upon completion of ozonation, the water is aerated.
How to determine the amount of ozone (K) in the water if you have an ozonizer:
K=(A*T):V.
— Where A is the device’s capacity in milligrams of ozone per hour (mg/h), T is the time in hours, and V is the aquarium volume in m3.
A positive effect from using ozone is achieved only with proper dosage. One should start with an ozone concentration of 0.1 to 0.15 mg/l of aquarium water per hour. The disinfection efficiency of ozone depends on contact time and dosage. Obviously, when used in an aquarium filtration system, ozone increases the efficiency of the biological filter and helps reduce problems associated with ammonia and nitrite spikes. The accumulation of organic pollutants in the water that are not broken down by the biofilter and cause a yellowish water tint, among other things, is significantly reduced. As for ozonation regimes, i.e., the required operating duration of the ozonating equipment and the frequency of its activation, only approximate recommendations can be given here.
Approximate, firstly, because for most cases the optimal ozone concentration in water has not yet been established; secondly, because during aeration only a portion of the ozone dissolves in the water, while some usually unknown amount escapes into the air; and thirdly, because the hobbyist does not always know the exact output of their ozonizer. It has been experimentally established that when treating water with ozone at a concentration of 15 mg/l, fifteen seconds was sufficient to reduce virus counts from 1 billion/ml to virtually zero.
Proper application of ozone in aquarium keeping involves certain challenges in dosage. Ozone oxidizes dissolved substances accumulated in the water. This leads to an increase in the oxidation-reduction potential. The cleaner the water, the higher the oxidation-reduction potential. To monitor the operation of an ozonizer supplying ozone to water, the method based on measuring the water’s oxidation-reduction potential rH is most often used. There is another widely used name for this parameter – “redox potential”.
The measurement of this potential is carried out similarly to pH measurement, i.e., using a millivoltmeter to measure the potential arising at a special platinum electrode. There is a relationship between the magnitude of the oxidation-reduction potential and the concentration of ozone in the water, so when dosing ozone, the redox potential is referred to, expressed in millivolts (mV).
Compared to industrial applications of ozone in water purification and sterilization, the range of aquarium ozone application is limited to 200-400 mV, which is significantly lower than the level used for tap water purification, where an adequate ozone concentration is within 600-800 mV. At the same time, it is generally accepted that complete water sterility is achieved already at rH = 700 mV. Redox potential monitoring is usually performed in the water flow at the outlet of the ozone-using device – most commonly a protein skimmer.
With a correctly chosen dose, nearly 100% mortality of harmful microorganisms can be achieved. Taking these circumstances into account, a hobbyist with no experience working with ozone can be advised initially to turn on the ozonizer twice a day, preferably morning and evening, for no more than 10-15 minutes. By observing the condition of the aquarium and the behavior of the fish, this time can gradually be increased to one to two hours per day. In bodies of water where fish are kept temporarily, such as during quarantine, the ozone concentration should be increased by 2-3 times (it is better to increase the number of sessions rather than their duration).
Disinfection is effective against pathogenic viruses and bacteria, microscopic fungi and protozoa, as well as against the ciliate *Ichthyophthirius* at the free-swimming “theront” (crawler) stage. It is also effective against *Oodinium* (flagellate) at the crawler stage. It is effective for destroying certain pathogenic organisms at the crawler stage, as well as in comprehensive aquarium disinfection once fish and plants have been removed.
Bloodworms and tubifex worms, which inhabit polluted wastewater, can be carriers of pathogenic microorganisms. They must be washed twice a day for 3-5 days before the first feeding to clear their intestines of harmful substances. For an extra layer of safety, the food is disinfected with ozone (0.5-1 h).
For the disinfection of newly acquired plants, it is sufficient to immerse them in freshly ozonized water for 20-30 minutes. Such water is prepared in a separate small vessel: ozone is bubbled directly through an airstone for at least an hour. Heavily ozonized water has a slightly bluish tint. Live foods are disinfected in the same way as plants. They are placed in freshly ozonized water for 10-15 minutes, preferably shortly before feeding them to the fish.
I want to warn you that an excessively high concentration of ozone in aquarium water, especially if maintained for a long time, can be dangerous to fish and plants. Therefore, one should not increase the duration of ozonation sessions without special need.
Water ozonation is especially effective when combined with other water purification methods. For example, water can be ozonized after protein skimmers or biological filters. Ozone is most commonly used in protein skimmer columns. In large aquariums utilizing a complex water treatment system, system elements must be configured correctly.
The optimal sequence is probably as follows: a mechanical filter and a protein skimmer remove about 80% of organic pollutants from the aquarium water. Next, the water should flow to a biological filter, be disinfected with ozone or ultraviolet light, filtered through activated carbon, and returned to the aquarium.
Water intake should be done from the surface, since aquatic life metabolites are lighter than water and accumulate as an oily layer near the surface. Purified water is best introduced from the bottom so that the water current lifts detritus from the bottom, which is then trapped by the mechanical filter. In a small aquarium (up to 300 liters), the units can operate independently of each other. For an aquarium with a volume of up to 200 liters that is sparsely stocked, a bottom biological filter alone is sufficient.
Water aeration in aquariums. How to reduce compressor noise.
Application of ozone in the aquarium. Bactericidal action of ozone. 
