By Bob Goemans
Site Supported in Part by:

The 'LIVING' Marine Aquarium Manual

Basic and Advanced Husbandry for the 'Modern' Marine Aquarium

by Bob Goemans

Chapter 3 - Water Processing Equipment

Keep in mind the equipment in this category differs from that in the following Chapter - Filtration Equipment, as these do not foster 'biological' processes, since their main purpose is to modify the elements and/or compounds passing through them. Lets begin with the calcium reactor.

(Please keep in mind all underlined word(s) are linkable files – just click on them and be taken to its content/photo. Also, all shown photos are clickable, which often allows a larger file to be seen.)


This equipment is mostly used on reef aquariums where control of alkalinity and calcium (Ca) are very important water quality parameters to its calcifying organisms such as corals, coralline/calcareous algae, snails, clams, and many other invertebrates. And where calcification is concerned, these two values, i.e., calcium and alkalinity are closely related to each other as one affects the other and vice versa, and furthermore, imbalances between the two often negatively affect coral health as explained further on in this book. In fact, these type 'reactors' are generally considered the easiest and safest way to maintain these and other important seawater elements and compounds for the larger more complex reef aquariums.

Their initial appearance may be to some extent intimidating and their cost somewhat high, yet overall they are fairly easy to use and quite cost effective in the long run. Furthermore, when compared to all other calcium and alkalinity control approaches, they require much less attention on a daily/weekly basis!

These mostly cylinder-shaped vessels had their beginning in the early 1990's, i.e., as a canister filter filled with coral gravel that used injected carbon dioxide (CO2) to dissolve its media, then send its calcium and alkalinity laden effluent to a reef aquarium (Hebbinghaus, 1993). The overall method continues to be used today with only some changes occurring in equipment design to improve efficiency. The chemistry associated with the device is discussed in Section Three - Seawater.

General Function

Using a dedicated pump, which often comes with the unit, and which is equipped with a multi-port fitting/arrangement located on its inlet side, allows water from the aquarium to enter via one inlet port and carbon dioxide from a pressurized bottle to enter via another inlet port. The pumps impeller then mixes them together and the water exits under pressure from the outlet side of the pump to a vessel filled calcareous gravel. This now pH-reduced water, about 6.0 - 6.5 slowly dissolves the media releasing small amounts of carbonates, bicarbonates, calcium, and some trace elements and flows out the unit under a small amount of pressure via an outlet tube and through small tubing back to the aquarium. Its flow back and into the aquarium is controlled with a small valve inserted into the return tubing and located somewhere along its length allowing for the drip rate into the aquarium water to be set at a desired rate/speed. Retailers generally sell the reactor body, which includes the pump and associated tubing and valves separately from a carbon dioxide bottle, and its needed regulator, solenoid and needle valve, which are also sold separately from the bottle itself.

Reactor Body

Whether cylinder shaped or not, look for a unit that has easy access to its interior, as the time will come to clean and refill it with new media. Since this is a slightly pressurized unit, look for a heavy gauge acrylic body that includes threaded fittings, which help prevent leaks.

Water Pump

Most reactors come with a pump, however, some are quite inexpensive and do not last long, besides being noisy. Look for a well known, high quality brand pump, and one that can easily be removed if service is needed.

Bubble Counter

This is simply a clear chamber that is usually filled with freshwater and which allows the hobbyist to monitor the flow of carbon dioxide gas bubbles entering the inlet side of the pump. It is supplied with most calcium reactors and is attached somewhere between the gas supply and its inlet to the pump. Most often, it's simply attached to the side of the reactor. Note, its freshwater will slowly evaporate, and this chamber will need refilling when it becomes too low. Filling with glycerol instead of freshwater is feasible and reduces its maintenance; nevertheless, freshwater is used by most hobbyists.

Somewhat different from average units, the Korallin calcium reactor has its bubble counter placed upside down, with reactor water continuously flowing through it on the way to the circulation pump. Carbon dioxide gas is released at its bottom via a tube passing through the top of the chamber, and rises upward into the pump. Therefore, the gas injection chamber, i.e., bubble counter, is always full of water, removing the need to refill it from maintenance chores.

Check Valve

Most bubble counters are fitted with a one-way check valve on their inlet side, which allows carbon dioxide to flow into the bubble counter from the supply bottle but no gas or liquid to flow in the opposite direction. This prevents any siphon effect from occurring if there was a power outage and prevents water from reaching the regulator. If the bubble counter does not have a check valve, one should be placed between the regulator and the bubble counter before proceeding.


A regulator controls the amount of gas that flows from the carbon dioxide bottle to the bubble counter. Most regulators have duel gauges, with each individually controlled. One gauge/range depicts the remaining level of gas in the supply bottle and the other, the delivery pressure. Most calcium reactors do not come with a regulator and it must be purchased separately, adding additional cost, as does the carbon dioxide bottle, which also is not included with most brands of calcium reactors.

It's also prudent to purchase a regulator that comes equipped with a 'solenoid.' This is simply an electrical device that will shut off gas flow when there is a power failure. If you purchase a regulator without a solenoid, carbon dioxide will continue to flow during a power outage. The flow of the gas could then evacuate the water in the reactor and eventually find its way to the aquarium, where it would result in a drastically lower pH, possibly killing everything in the system.

Regulators should have a high quality needle valve for precise control of the amount of carbon dioxide leaving the regulator. However, some come only equipped with a low cost valve that makes it somewhat difficult to 'precisely' set a desired flow rate, i.e., to narrow the flow to a more exact number of bubbles instead of a 'stream' of bubbles. Having a regulator with more precise control may be somewhat more costly than an inexpensive unit; yet having precise control prevents wasteful use of carbon dioxide and much better control of the reaction cylinder's effluent parameters.

Supply Bottle

Most calcium reactors do not come with a carbon dioxide supply bottle. If thinking of buying the supply bottle through a mail order company, keep in mind it will arrive empty, as it cannot be shipped with compressed gas. And before being purchased this way, be sure it can be refilled at a local welding supply company, as it may be the local welding company will not want to refill a bottle they have no safety record on. Bottles come in different sizes, e.g., 5, 10, 15, 20 pounds and larger, and most companies selling welding equipment can supply them. In most applications, the gas in a 5 pound bottle servicing a 180-gallon reef aquarium should last for a few months.


Most hobbyists use normal airline tubing, however, it is slightly porous when it comes to carbon dioxide. Since the physical size of the carbon dioxide molecule is capable of somewhat passing through the material that composes regular airline tubing, some will be lost to the atmosphere. Silicone tubing is somewhat better, but the tubing sold in medical supply stores for just said purpose, i.e., supplying carbon dioxide, is better suited.

Leak Checking

Once the bottle, regulator and tubing is pressurized it is prudent to leak check all the fittings. Simply add a few drops of liquid dishwasher soap to a half-cup of tap water and stir. Using a small brush apply the liquid around all the fittings. If there is any escaping gas, foam will be produced. Simply retighten and recheck the fitting.

Design Updates

There have been many improvements in original equipment design. One of the earliest was that of adding a second media filled cylinder to somewhat boost the pH of the effluent reaching the aquarium. Effluent from the first cylinder was usually about 6.0 - 6.5, and from that of a second cylinder about 6.7 - 7.0 and at the same time, adding a small amount of additional calcium and alkalinity ions to the effluent flowing to the aquarium. Two-cylinder units of course are more expensive, nevertheless many aquarists considered raising effluent pH well worth the added expense.

Direction of internal reactor water flow, i.e., top to bottom or bottom to top is another aspect to take into consideration. Since the media dissolves, fines are better kept somewhat elevated in the media using an upward flow design, thereby possibly preventing settling/clogging of the lower media, possibly leading to channeling of the water flow. Channeling would reduce unit efficiency, as water flow would then be through narrow passageways instead of evenly through all the media. Units using the top down flow method have a sponge filter at the bottom of the media to prevent fines from clogging the inlet of the bottom located stand-pipe/outlet tube. Those with the up flow method usually have a screen or sponge filter at the top of the cylinder to prevent reduced size media from entering the outlet at the top of the cylinder.

The possibility of excess carbon dioxide entering the aquarium may have been resolved by the German Company Schuran, which places a small chamber at the top of the reactor where excess gas can collect and be passed back to the inlet side of the equipments circulation pump, where its flow is then sent to the 'bottom' of the reactor. Besides collecting excess carbon dioxide and keeping it out of the aquarium, it results in a more efficient use of the gas.

Another novel approach, one that uses a fine, uniform sized calcareous media in an upward flow 'fluidized' fashion has been introduced by the Deltec Company. Similar in operation to the up flow fluidized bed devices used for biological filtration, this equipment uses special spherical sized calcium carbonate particles to prevent channeling, and is said to provide increased efficiency over that of conventional methods. In fact, regular aragonite sand might be usable if sized correctly. This highly efficient method of dissolution may allow small units to adequately provide for moderate to high levels of calcification in fairly large aquaria.

Effluent Parameter Control

As for a carbon dioxide bubble rate and speed of the drip rate of the now treated water returning to the aquarium that of course depends upon tank size and its demand for calcium and alkalinity, and the quality of the chosen media. Nevertheless, for beginning almost any large aquarium, e.g., 100 gallons or larger, I've found a bubble rate of 60 per minute and a drip rate of 110 drops per minute a fairly good starting point. Also recommend testing every other day the effluents alkalinity and adjusting carbon dioxide bubble rate accordingly to maintain a level of alkalinity three times that desired for the aquarium, e.g., if desired aquarium alkalinity was 2.5 meq/l (7dKH), the effluent should be 7.5 meq/l (21 dKH). At the same time test aquarium calcium and alkalinity and adjust the drip rate as needed to maintain its desired level. Once set, testing can be reduced to once every 10 days to two weeks.

As for the media itself, usually within 10 months the difference between alkalinity and calcium levels in the aquarium may begin to widen and adjustments to drip rate and carbon dioxide dose not fixing the situation. Changing the media, even though it still 'looks' okay is highly recommended because the calcium was the first to dissolve in the media, with carbonates that are slightly harder remaining and slowly making up the majority of the now entering constituents in the effluent.

Furthermore, consider covering the reactor cylinder with some sort of material to keep light from generating an inside alga growth. Light plus the equipments internal nutrients can lead to an unsightly internal alga growth and additional maintenance the next time the media is replaced. Choices of media are discussed in Section Three - Chapter 11.

Reverse Osmosis

Freshwater is used to replenish water that has evaporated and/or for water changes. Unfortunately tap water sometimes contains elements and compounds that even though not harmful to humans can be harmful to aquarium inhabitants. Levels of nitrate (NO3), phosphate (PO4), and silica (SiO2) in tap water may be high enough to generate unwanted algae growths, those of which are especially more damaging in reef aquariums. Small amounts of copper (Cu) in the incoming water supply could also be high enough to kill invertebrates, yet not harmful to humans. Therefore many hobbyists find it necessary to first process tap water before using it in their aquariums.

Reverse Osmosis (RO) is a water purification process that removes about 90% of unwanted dissolved salts and organic compounds. The process was first discovered being used by sea birds. It was noticed that sea birds would drink seawater and appear to be unaffected by its high salt content. Upon a closer look it was found the birds actually filtered the seawater through a membrane in their beak, resulting in only freshwater being taken into their systems.

For our purposes there are basically two types of membranes used in commercial RO equipment: cellulose triacetate (CTA) and thin film composite (TFC). The TFC membrane is far superior in that its rejection rate of pollutants is much higher, about 90% depending upon the particular pollutant and it does not readily breakdown from bacterial attack.

Since the membrane is the heart of the RO system it must be protected from certain impurities and/or disinfecting compounds in the in-coming water supply. To protect the membrane from coarse solids that would quickly clog the very small holes in the membrane, water should first flow through a Sediment Prefilter. Next, an in-line filter should be installed with activated carbon or preferably a carbon block as the filter medium. Since TFC membranes are very sensitive to chlorine and water supply companies generally use chlorine to disinfect water lines, a carbon prefilter is a must. Besides removing chlorine and pesticides, other volatiles and heavy metals will also be removed.

Water then flows to the membrane where, via the water pressure in the municipal water system, only very small almost pure water molecules can pass through membrane holes. Larger contaminant molecules cannot fit through these tiny holes and are rejected via a drain line. Nevertheless, all RO membranes have difficulty in rejecting nitrate and silica, which are two of the three major plant nutrients. Phosphate, the third plant nutrient is rejected much better, however certain conditions can also make it difficult to remove.

The only minor drawback with many RO units is many only provide one usable gallon of water for about every three to five that flows through them. Yet, it seems like the more water rejected the better the membrane performs and the longer it lasts. Nevertheless, the reject water is still usable for watering plants and/or for use in Cichlid aquariums.

No matter what brand is chosen there should be an individual replaceable sediment and carbon prefilter along with a quality brand TFC membrane. Depending upon usage most carbon filters should be replaced every six months and the sediment filter once every year. The RO membrane can last for many years.

In fact, to judge when its time to change the membrane, read what the Total Dissolved Solids (TDS) is when entering the membrane. Once outgoing TDS exceeds 2 per hundred going into the membrane, it needs to be changed. So, ...if 300 is going in, and less than 6 is coming out, it's still okay. But once getting to 7, after running for about twenty minutes, than it should be changed. Battery operated TDS meters are quite inexpensive and its worthwhile to have one!

General use aquarium RO units are rated in how many gallons they can produce in a twenty-four hour period. Usually the 10 to 50 gallons per day units will supply most hobbyist needs. Water pressure is an important operating parameter and 45 pounds should be considered minimum, 55 pounds very good, and 65 pounds ideal. In many areas an RO system is a worthwhile investment, and since product improvements keep coming, thoroughly checkout the unit thought to fulfill your needs prior to purchasing it and compare it to other brands. Yet keep in mind to have the quality water needed for most reef aquariums, the effluent from an RO unit should then be flowed through a DI unit – the next piece of equipment to be described.


This equipment uses specifically tuned resins to attract unwanted compounds and elements thereby selectively removing them from the water that passes through the unit. Deionization units, or IX equipment (Ion eXchange) as they are sometimes called in the trade, are sold in two different styles — a mixed bed of both anion and cation resin in a single container/cartridge or separate beds of each type resin each in its own container. Anion resins attract negatively charged ions and cation resins remove positively charged ions. There's also no reject water as there is with RO units and what passes through DI units is 100% usable.

Now don't go out and buy a DI unit and then throw out your RO unit. It's actually better to first process water through an RO, and then process it through a DI unit. That's because tap water is normally high in many of the anions/cations a mixed or separate bed unit removes. When resins in separate bed units become clogged with unwanted ions they need to be recharged. Only lye can be used to recharge an anion resin, and acid to recharge a cation resin. Therefore only separate beds can be recharged and much care needs to be taken when using dangerous recharging solutions along with the disposal of their spent solutions when the task is complete. Mixed bed cartridges are simply replaced with new cartridges. Frequent servicing and/or unnecessary cartridge replacement is greatly reduced when water is first processed through an RO unit.

Until recently DI unit resins did not truly remove all remaining plant nutrients that slipped through an RO unit. Colloidal silica totally slipped through DI resins because the RO process reduces the pH of the incoming water. Some other plant nutrients in this reduced pH stream, about 6.3, also slipped through. The SpectraPure Company is one of the leading manufacturers of quality water processing equipment to have addressed this problem in bringing out a DI unit that uses a special resin to boost pH of its incoming water and effectively remove any remaining nutrients. In fact its product water is rated at 18 megohm (high quality water)! Therefore, a DI unit using the effluent from a RO makes very good sense, and some manufacturers have combined them into one unit, such as the SpectraPure Silica-Buster/MAXCAP UHE 400 RO/DI systems.

On the unit described above, one can judge the remaining effectiveness of the RO cartridge (next to last cartridge) and the DI cartridge (last cartridge) by reading the TDS going into the 'DI' cartridge. Going in should not be above 3 and/or anything above 1 coming out is a need to change both cartridges! In fact, a good rule of thumb for all brand units.

Sterilization Equipment

Water sterilization in marine aquariums can be easily accomplished by ultraviolet irradiation and/or with the use of ozone. Besides killing free-floating alga cells, parasites, and viruses, sterilization methods can also kill free floating beneficial bacteria. Equipment such as this can be considered supplemental and not essential to the wellbeing of the aquarium's inhabitants.

Ultraviolet Sterilization

Ultraviolet is a word assigned to the light wavelengths found just below the visible portion of the spectrum, i.e., between the blue violet and x-ray wavelengths, which are 100 - 280 nm. And its the 253.7 nanometer (nm) wavelength that is most effective in destroying most free-floating bacteria, virus, fungi, mold, and very small protozoan, and which is measured in microwatt seconds per square centimeter (uW/cm2). Correct dosage timeframe and level of intensity will prevent reproduction in some organisms as it breaks the DNA chain, therefore, its also used to sterilize water and make meats safer to eat for human consumption. And since there is no harm to fishes in the aquarium or the chemistry of its seawater, it's widely used throughout the freshwater and marine industry. Yet it can alter or change the chemical structure or nature of some medications therefore its widely recommend it be disabled while medication treatments are being utilized.

There are different thoughts as to how much UV energy is needed to destroy various entities, with 15,000 uW/cm2 considered minimum for algae, bacteria and viruses, and 35,000 uW/cm2 considered minimum for effective destruction of larger protozoan (Spotte 1979). However, more recent information indicates that even higher concentrations of exposure may be required. Pete Escobal, in his book "Aquatic Systems Engineering: Devices and How They Work" (Dimension Engineering Press; Oxnard, CA.; 1996) indicates that although many bacteria and viruses are effectively killed at 15,000 uW/cm2, some will require between 20,000 – 25,000 uW/cm2. In fact, he goes on to say the Tobacco Mosaic virus requires an astounding 440,000 uW/cm2 for eradication, and that Paramecium requires about 200,000 uW/cm2 in order to be killed. Nevertheless, Don Conwell, of Emperor Aquatics ( states that 90,000 uW/cm2 is really all that is required to eradicate most protozoans, since at that level of concentration; it prevents replication of the parasites.

Be aware that UV light is detrimental to the human eye; therefore never look directly at a lit UV lamp. Furthermore, just because the lamp is lit and giving off a color/blue light does not mean it is operating correctly, as UV itself is actually invisible to the human eye. Another interesting aspect is that the effective range of the wavelength is quite short, therefore to destroy organisms the water flowing past the lamp must be quite close, e.g., about 1 inch (2.5 cm).

As for the device itself, a quartz (preferably) or thin crystal glass sleeve/tube encloses a germicidal lamp and filters out all UV wavelengths except the 253.7 wavelength. This sleeve also helps to insure a proper operating temperature, e.g., 104°F (40°C), and by preventing water from coming in contact with the lamp, prevents a bio-film from forming on the lamp itself thereby reducing lamp maintenance to nothing more than replacing the lamp when necessary. And as to dwell time, i.e., the length of time water stays inside the unit, which is very important, it must remain long enough to kill the targeted organisms. Therefore manufacturers provide the data necessary for making the correct model choice when it comes to your purpose/aquarium.

As to some helpful hints, decreasing the flow rate through the unit or changing its flow turbulence by mounting the unit vertical may help kill larger parasites because their UV absorption level becomes greater. And do not use when starting an aquarium as it would simply kill any nitrifying bacteria in the bulk water and lengthen the cycle time. And if at all possible allow only filtered water to flow through the device as it will increase the actual efficient operating time since the sleeve will have to be cleaned less often. And last but not least, shut the unit off while doing water changes because should cooling water flow cease while operating, the lamp may get too hot and burst causing a hazardous condition to all concerned!

This is another piece of equipment where one has to ask 'is it really needed?' I like to look at it like it's an insurance policy - nice to already have if a problem requiring its capability arises. Therefore tend to think it's a wise tool for fish-only aquariums, but where reef aquariums are involved, where its inhabitants are filter feeders, the destroying of the free floating organisms utilized by its animals is not recommended as a tool to use full time. AquaTop makes an interesting combination hang-on-tank (HOT) UV that is incorporated into a HOT filter unit, making it quite easy to get up and running when needed!


Lets begin with an explanation of ozone, then why some aquarists use it, and also some of its good and not so good aspects, then proceed to the equipment used to generate it, which are sometimes referred to as an 'Ozonizer.'

Ozone differs from the normal molecule of oxygen (O2), which has two atoms, since it contains one additional atom (O3). This makes it an intense oxidizing agent because that third atom is highly unstable and will react with various organic and inorganic molecules chemically and therefore destroy parasites and bacteria. In excessive amounts the human nose can detect it because it smells similar to overly ripe fruit. As to its flow, it's measured in milligrams per hour (mg/h).

As for use in aquaria its often applied as a way to reduce unwanted dissolved waste products, which if allowed to accumulate would greatly reduce water quality. By monitoring system Redox, i.e., 'reduction/oxidation' with an ORP meter, and applying a given amount of ozone as needed a sequence of chemical events occur. In said process, elements and compounds transfer or rearrange their electrons (oxidation/reduction) and those wanting to gain an electron are called 'reduction agents' whereas those wanting to give up an electron are called 'oxidizing agents.' Again, the whole process can be measured with an Oxidation Reduction Potential (ORP) meter which denotes the effectiveness of the process in a minute electrical charge that it generates in millivolts (mV).

One could say the process is similar to the resistance in electrical wiring, i.e., the more resistance in the wire carrying the current, the less amount of electric current reaching its intended target. Basically, it's the same in the aquarium, as dirty water has less ability/potential to conduct electricity. As a good comparison, the water around outer coral reefs has an ORP of 350 to 400 mV and corals that come from lagoon areas mostly experience an ORP of about 200 to 300 mV.

I have prepared the following chart and have widely made it available to those interested;



<100 mV Very Poor

100 - 200 mV Poor

200 - 300 mV Good

300 - 400 mV Very Good

400 - 450 mV Excellent

>450 mV Risky

One should keep in mind that even though there are some good points in its use, there are also some negative circumstances that should be understood before using this powerful oxidizing agent.

Where systems are low in ORP there's no doubt the oxidation of suspended matter/dissolved organic material will increases Redox readings, and at the same time help promote a crystal-clear water column. And since it oxidizes nitrite, it may also help keep nitrate levels somewhat lower. That can help lower unwanted algae problems, and it will also kill alga spores, some free-swimming parasites, and various forms of bacteria, good or bad. And in small amounts when fed through a skimmer, e.g., 5 mg/hr/25 gallons of water flowing through a protein skimmer, it can enhance skimmer foam production. Nevertheless, when more than this amount is used it will decrease skimmer foam production. And of course, as mentioned above, it cannot be used when medicating.

On the dark side, 'more is better,' is definitely not the rule here! You do not want to use it while beginning an aquarium system, as it will kill nitrifying bacteria as they are being dispersed through the water column. Leakage into a room can cause human disorders such as headaches or nausea and/or negatively affect the human eye. And if there is a 'desired' alga, it could eliminate or reduce its growth. Also, one needs to keep in mind it reduces the integrity/composition of plastic and rubber products.

As to how to apply this powerful oxidizing agent, for best results it should be dispensed through a protein skimmer, as that allows maximum utilization of the gas because of the air/water mixture inside skimmers. And if doing so, keep in mind the effluent coming from the skimmer contains some residual ozone, which if allowed to enter the aquarium untreated may cause some damage to fish tissue and invertebrates if in any sizable amounts. Even though short-lived, maybe up to an hour, to alleviate such a possibly the effluent should be passed over a bed of activated carbon, which will remove the residual ozone before it enters the aquarium.

Some manufactures make ozone test kits, or you can use a simple swimming pool test kit that tests for total chlorine or DPD 3, which is suitable for assuring this aspect is within safe operating parameters, i.e., not to exceed 0.05 ppm for fish or 0.02 ppm for invertebrates (D. Vaughan, pers. com.).

One further thought to keep in mind is that when ozone is produced in areas of high humidity, its effectiveness will be reduced, sometimes as much as 50%. To overcome that, first flow the air through an inexpensive air dryer before allowing it to enter the ozone producing equipment. And don't forget to use ozone safe tubing, as ordinary airline tubing will not remain in good shape for very long!

Probably, a good question to ask oneself is it really needed! Unless overcrowding and/or over feeding, I think most aquarists can get by without it. And even if its thought to be needed, would first suggest increasing water circulation to increase dissolved oxygen, maybe reducing bioload if overcrowded, switching to a more efficient protein skimmer, and if using a trickle filter, placing some airstones under its trickle section. Overall, at least first try improving the general level of maintenance.

If used to help control various pathogenic bacteria (Aeromonas, Pseudomonas, Vibrio), viruses, and protozoans, keep in mind it can reduce them, but probably not eradicate them. And remember its effectiveness is based on a number of factors, such as contact time, flow rate, humidity where produced, and the amount of suspended organics in the water. Bottom line, being able to discern the system's Redox/ORP is an important factor, and when ozone is properly utilized, if really needed, it will help maintain decent water quality. Furthermore, properly controlled/metered amounts of ozone should not present any problems to fish and invertebrates.

Ultraviolet Ozonizer

This type ozonizer uses a UV lamp that produces a very short UV wavelength of about 200 nanometers. The UV lamp is contained inside a chamber that allows air from an air pump to flow past it. The UV light interacts with the oxygen molecules flowing past it and forms ozone. The level of ozone produced gradually diminishes as the lamp ages. Most UV lamp ozonizers are simple airflow devices. Except for lamp replacement, there's no maintenance.

Corona Discharge Ozonizer

Most ozonizers are this type where ozone is produced by passing air from an air pump past two electrodes separated by an insulator. Electric current is alternated between the electrodes but cannot pass through the insulator. When polarity is reversed the electrons on the surface of the insulator arc and that arc interacts with the oxygen content of the flowing air, producing ozone. Most of these type ozonizers are equipped with a variable control that allows the electric current to be regulated resulting in various levels of ozone.

Because of the electrical spark inside the device, a residue of minerals will buildup on the surface of the metal electrode. Just like some spark plugs in a car engine they should be cleaned regularly or ozone output may diminish. Some quality ozonizers come with instructions and a tool kit to accomplish regular maintenance. If possible, disassemble every six months and wash the glass electrode with a mild detergent and brush the metal electrode with a metal pipe brush. Remove any dust, dry the parts and reassemble.

As with all ozonizers there should be a check valve located in the air supply line between the air pump and the ozonizer. It should be installed whether the ozonizer is located above or below the aquarium. If located below the aquarium a check valve will prevent a siphon effect of aquarium water if there is a power loss and prevent it from reaching the ozonizer. When mounted above the aquarium, a power loss can initiate a siphon effect of the ozone gas itself into the air pump, destroying any plastic/rubber parts of the unit.

Air Dryer

Humidity reduces the efficiency of an ozonizer; therefore it's important to first pass the air supply through an air dryer before it flows to the ozonizer. This is a very simple device, usually a clear plastic tube filled with desiccating beads. The beads turn pink when saturated with moisture and can simply be recharged by removing them and heating in an oven at 350°F. This drives the moisture back into the air (and your spouse crazy) and the beads can be reloaded into the dryer chamber. If you have high humidity in your home and you do not use a dryer, your ozonizer's efficiency may be reduced by approximately 50%. Air dryers are low cost items so don't put off having this piece of equipment if you decide to use ozone.

Redox Controller

Is the purchase of an air pump, air dryer and ozonizer the end of your equipment purchases when this type equipment is employed? The answer would be 'YES' if the ozonizer came complete with a 'REDOX controller.' Keep in mind the requirements for ozone change hour by hour in the closed system, therefore, its safer for everyone concerned to have a 'controller' that will allow ozone to flow 'as needed.' Such a device is called a Redox Controller. Some ozonizers come completed with the controller and its special ORP probe, which when submerged in the aquarium's water sends an electrical reading of the waters dissolved compounds/elements to the controlling device. By setting the controlling device's minimum and maximum electrical levels, ozone will be automatically turned on/off for a given degree of 'sanitizing.' Generally, levels between 300 to 400 mV should suffice for most aquariums.

However, if the unit purchased does not have a controller, then one needs to manually set the degree of sanitizing thought needed! And yes, there's no doubt the eye and nose of an experienced hobbyist can judge system conditions. The eye sees the general condition of the animals; color/clarity of the water and the nose knows when an excessive amount of ozone is flowing. Not very scientific, but useful. Nevertheless, the addition of a redox controller and its platinum coated ORP probe is 'highly' recommended!

Adding Ozone Directly

Adding ozone directly to the aquarium water is very risky at best! Ozone is usually dispensed through a reactor or protein skimmer. The effluent from these devices then flows over activated carbon and when residual ozone comes in contact with the carbon, its third oxygen atom is neutralized. If some residual ozone slips by the carbon it will stay active for up to an hour in the aquarium where it can destroy bacteria and damage animal tissue. Even though ozone is a highly oxidizing substance I personally know of some hobbyists that dispense it through airstones located under the trickle section of their wet/dry systems. They claim it is an easy way to raise ORP level and does not interfere with protein foaming. They also claim it results in a better aquarium environment without the need to purchase a controlling device. Yet, putting ozone directly in the aquarium, in my opinion, is like playing Russian Roulette - you may get past the first few pulls, but!

Oxygen/Ozone Reactors

Depending upon where you live in this world these are still occasionally seen these days, which in my opinion is unfortunate to some extent from what I know of their usage/history in some far past applications. Not only were there explosions with some units and personal injuries, many aquarium wipeouts were experienced. And yes, it could be said in the hands of a truly experienced person those would have probably not occurred, 'but' nevertheless these, depending upon their complexity are tricky devices and require precise setup, operation and frequent tweaking!

These type reactors for increasing dissolved oxygen were from my past experience with those having them, usually canister-shaped. Aquarium water would flow into these devices through the top of the unit and be sprayed or trickle over the unit's internal packing, e.g., bio-balls, which usually filled most of the unit. Air from a high quality air pump (supplying either regular air or ozone) would enter the top of the unit. When internal air pressure exceeded normal atmospheric pressure, the over-pressure pushed on the surface of the water inside the unit and drove its water content up a vertical standpipe where it returned to the aquarium. Air pressure inside the unit controls the water level in the unit, which was usually maintained at about 2 inches. The stronger the water flow the more forceful the air pressure had to be to maintain correct internal water level.

Under pressure, which was about 1.5 to 3.0 PSI for ozone or 3.0 to 5.0 PSI for regular air, either will enter the thin film of water flowing over the units packing material. An air pressure gauge mounted on top of the unit allowed internal pressure to be monitored. An adjustable valve on the air supply line controlled airflow. Under increased atmospheric pressure the water inside this device could hold a higher level of gas (ozone or regular air) than under normal atmospheric pressure. This is referred to as supersaturation. This highly oxygenated water then flows back to the aquarium where the additional oxygen improves its redox potential.

These type devices were/are highly dependent on the quality of the air pump since it must be capable of maintaining a steady pressure inside the reactor. Too much pressure will drive all the water out of the unit and allow the gas to discharge directly to the aquarium. Too little pressure would allow the reactor to fill with water canceling out its benefits and possibly allowing water to flow to the air pump.

If normal air is being supplied, the supersaturated air is dispensed right back to the sump/aquarium, however, if ozone is used, keep in mind most air pump diaphragms are not ozone safe. Therefore, it was/still is a good idea to install an ozone resistant check valve between the air pump and the ozone generator. Also, since the decay rate of ozone is faster than the water's absorption rate it was/still is recommended the water level in the reactor be operated at almost fully evacuated. Keep in mind its effluent now possibly carrying a 'considerable' amount of ozone should be passed over activated carbon before entering the sump/aquarium. And since reactors were/are not sold with air pumps, ask the manufacturer of the unit for their recommendation.

As to using/adding medical grade oxygen to a reactor, that can be extremely toxic to both fish and invertebrates, therefore totally disregard its use!

Regular air is probably the best choice for most hobbyists if this type equipment is of interest, yet if ozone is the choice, be sure the reactor is ozone proof.

Even though it's said reactors are more effective for dispensing ozone than a protein skimmer because ozone, if dispensed at a too high level interferes with the skimmers foam formation, they are more technically advanced and require a high level of expertise to operate, far more than operating a skimmer! Its also said dispensing ozone through a reactor provides a sanitizing effect in addition to the higher oxygen content of its effluent. But don't misread that, as the additional atom of oxygen is short lived and does not really add any useful additional oxygen, i.e., more dissolved oxygen than what would be supplied by regular air, to the aquarium.

If tempted by this type equipment, and still available in your neck of the woods, carefully follow manufacturer instructions for their set-up and maintenance, but keep in mind, in the wrong hands it can quickly get out of control and ruin a perfectly good aquarium. Only very experienced aquarists should consider these devices.


Lets now turn to Chapter 4, which discusses 'Filtration Equipment.'