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Using Ozone in the Home Aquarium

The use of ozone has long been a standard practice in industrial and public water purification plants, and large scale public aquarium filtration, as one of the best and most efficient means to increase water quality, while still being able to promote water conservation.   One of the biggest problems to overcome in these closed water systems is the accumulation of dissolved organic waste from various biological sources such as animal waste and decomposing food and plant material.
In aquariums of any scale, mechanical filtration will remove large organic and inorganic solids, and biological filters will remove dissolved organic material in the form of Ammonia and Nitrite, this still leaves behind a large number of other dissolved and colloidal organic materials that will accumulate over time (the ones causing colors and odors being most noticeable).  In most cases these materials are only removed by physical water changes, or chemical absorption media.  While frequent water changes may be practical for removing these dissolved materials in smaller aquariums where you are not dealing with large volumes of water, it is not a practical method for removal of these materials in large systems or in systems where water conservation is at a premium.  Using chemical absorption media is expensive, and is limited in is ability to remove all of these undesirable dissolved organics.  This is where the use of Ozone comes in, I will try to answer some basic questions about ozone below

So, what is ozone, and how does it work to remove these dissolved organic molecules?
Ozone is a naturally occurring highly reactive form of oxygen gas comprised of three oxygen molecules (O3) that is also highly unstable and short lived.  It is this inherent instability of the ozone molecule that is taken advantage of for use as a strong oxidizing agent.  “Normal” oxygen, as found in air and water, has two oxygen molecules (O2) and is very stable.  When ozone molecules break down, they lose an oxygen molecule, forming a stable “normal” oxygen molecule, and a free single oxygen atom.  It is this free oxygen atom that attaches to dissolved organic compounds, which in turn causes them to break down into simpler forms that can consumed by heterotrophic bacteria , or recombine into forms that can be removed with mechanical filtration or protein skimming.  The organic molecule that gained the free oxygen atom and subsequently broke apart is now said to be oxidized.  This is a bit of an oversimplification of the process, but it is a about as general an explanation as I can give without losing too many of you. (and myself, chemistry was never my strong point)

How do I get ozone, and how do I use it in my aquarium?

As I have already discussed ozone is a highly unstable gas, so it is not possible to store, or purchase ozone, it only has a life span of a few seconds before it breaks apart.  Ozone needs to be generated as needed with a device called an ozonizer or ozone generator.  Most modern units available for the aquarium hobby use a Corona Discharge method to create ozone. In a Corona Discharge unit, air is passed through a strong electrical field which causes atmospheric oxygen (O2) to break apart into single oxygen molecules.  Some of these oxygen molecules will then combine back together after passing through the electrical field to form Ozone (O3).  This generated ozone gas must then be quickly used before it breaks apart again.  Most marine aquarium hobbyists already have the perfect piece of equipment for introducing ozone into their aquariums, their protein skimmer.  Ozone needs to have contact time with the water so that it is exposed to the materials that you wish to oxidize.  Fractionating the ozone gas by drawing it into the air intake of your protein skimmer, you can use your skimmer as a highly efficient contact chamber.  This works for both venturi type, and air pump driven protein skimmers.  You need to make sure that your skimmer is made of ozone safe materials, and that you use ozone safe air tubing.  Some plastics and rubber can be damaged by ozone, and cause leaks or failures if exposed for prolonged periods of time.  There are also ozone reactors available, but they are a bit more difficult to use, and harder to find.

How much ozone needs to be used, and is it safe for aquarium inhabitants.

The best way to monitor and control ozone is with the use of an ORP monitor or controller.  ORP stands for Oxidation Reduction Potential, and In terms of your aquarium water, it reads an electrical voltage in Milli Volts (mV) which measures the oxidation ability of the water.  As Ozone is applied the ORP level increases.  Natural sea water has an ORP value of 350-400 mV.  ORP levels of 200 or less in your aquarium are indicative of low oxygen, high dissolved organic, conditions.  By monitoring the ORP level in your aquarium, and maintaining it between 250-350mV, you can adjust your ozone dosage accordingly. Using an ORP controller simplifies this process to shut off you ozone generated at a desired ORP level.  You should never exceed an ORP of 400mV in your aquarium.  Ozone units like the Red Sea AquaZone Plus have a built in ORP controller.

Most manufacturers of ozone units recommend a dosage rate between 5-15mg per hour per 100 liters (26 gallons) many different size units are available, so you can choose an appropriate output unit for your size aquarium, and most have a variable output.  Controlling your ozone output is very important, too much is not a good thing; very low doses will provide you with excellent results in most cases, overdosing can be harmful to both you and your aquarium inhabitants.  There are several methods to make sure that you are applying the correct amounts of ozone into your aquarium.  The goal when introducing ozone into your protein skimmer is for all of the ozone to break down in the chamber or escape through the top of the skimmer.  You do not want ozone to escape freely into your aquarium, it will also oxidize organic material in there, which will cause damage to fishes gills, and invertebrate tissue.  You also do not want high concentrations of ozone to escape into the air; it is harmfull to your lungs if in high enough levels.  Most hobbyist units do not produce dangerous levels of ozone.  You can use carbon in your sump chamber that the skimmer discharges into, or on top of your protein skimmer to absorb residual Ozone, and use an Ozone test kit to make sure that none is escaping the reaction chamber into your aquarium.  Overdosing Ozone can also produce some harmful compounds, mainly in the form of hypochloric and hypobromic acids, this is why you should not exceed and ORP of 400 mV It is a not a good idea to use ozone in small confined spaces, a well ventilated room or aquarium cabinet should be considered.  If you are not using an ORP meter or controller, a conservative approach should be used, stick to the 5mg per hour, per 100 liter rate to be safe.  Another caution when using ozone is to use an air dryer to make sure that the air that is drawn into the ozone generator is dry, a simple and effective unit like the Red Sea Air Dryer, uses regenerable desiccant  beads to draw moisture out of the air.  Moisture can react with Ozone to create nitric acid, which can damage equipment, and lower the pH in your aquarium.

What are the benefits of using ozone?


Water clarity is the number one reason most people use ozone.  There are many dissolved organics that can discolor your water, ozone will oxidize these and produce water that is crystal clear.  This is especially beneficial to reef aquariums where light penetration is crucial.  Many people do not even realize how discolored their water is until they see the difference ozone can make. Ozone also has disinfecting properties, pathogenic bacteria, single cell parasites and algae, viruses are all destroyed by contact with ozone.  Increased dissolved oxygen levels from the reduced organic load and bacterial oxygen consumption.  Ozone will destroy pesticides, detergents, and many other toxins that may be in your tap water.  Many organisms release substances that are intended to defend themselves, or inhibit predators or competitors that can accumulate over time and become problematic will be destroyed by ozone.  Ammonia and Nitrite are oxidized into less harmful Nitrate when exposed to Ozone.  And as mentioned previously, using ozone can reduce the amount of water that needs to be changed in closed systems.



I hope that this has shed some light on Ozone use in the home aquarium, and that I answered some of the questions that you may have about Ozone use.  Feel free to leave comments if you’re looking for any additional info.


Until next time,




  1. avatar

    I have a large 800 lelitre aquarium with fresh water with discus & other fish. It has fine gravel driftwood and well planted. I have a large ozotech & controller skimmer in the sump. Could you please tell me what levels of ozone for fresh water I should use & if you have other imformation.Grant.

  2. avatar

    For freshwater, I would reccomend keeping to the lower end of the scale for ozone use. 5mg per hour, per 100 liters. Introduced through your skimmer in the sump. With ozone use in any system, it is always smart to be conservative. Start with your unit at its lowest setting, and see how much ozone is needed to raise your ORP to the 300-350mv range. Every system is going to act differently depending upon its given organic load.

  3. avatar

    I have a frequent problem with unwanted algae in a reef tank an wanted to know if ozone will help. I do my 10 % water changes bi weekly with r/o & deionized wter.

  4. avatar

    It depends on the type of algae you’re having a problem with. Ozone will oxidize dissolved organic waste, so it will help control slime algaes, and maintain overall water quality. But will not directly effect higher forms of algae established in the aquarium. I would recommend looking at Nitrate, Phosphate, and light quality and duration as a cause for the algae before installing Ozone as there may be another issue to address to fix the problem.

  5. avatar

    I have a 140G fresh water discus tank. I tend to go overboard in buying equipment and would appreciate your recommendation for the appropriate ozonizer system model that will meet my needs.


  6. avatar

    From an equipment standpoint, using Ozone on a freshwater aquarium can be a bit more difficult to use. To use ozone, you need some sort of a reaction chamber to introduce generated ozone to the aquarium water. In Marine aquariums this is easily accomplished with the use of an appropriate protein skimmer in the sump of the filtration system. If you use a sump type, or wet dry type, filter on your discus tank, then you can use the same method. Even in a freshwater aquarium, a protein skimmer will still act as an efficient reaction chamber.
    If this is not an option for you, then you may be better off using Chemical media, Reverse Osmosis water, and Ultraviolet Sterilization to acheive an low organic load on your system.


  7. avatar

    Took me ages to find this post, this time I’ll bookmark it.

  8. avatar

    My set up is a 140G fresh water, WS-300 Eshopps wet/dry sump, and do use RO water. In preparation, I did purchase a protein skimmer. Do I need a charcoal reactor as well for the final step on the return to prevent O3 from going back into the tank?

    Any advice on how to set components up and the a recommended system for my purposes at TFP?

    Thanks so much!

  9. avatar

    Residual ozone is not usually a problem if you are dosing conservatively, especially if you are using an ORP controller to control you ozone unit. Using a carbon reactor can be used, and will have other benifits beyond that of absorbing any residual ozone. If you are planning on heavily dosing ozone, or are using an oversized ozone unit, then you may want to consider using a carbon reactor as a failsafe for your system. The other thing to make sure that you are doing is properly adjusting your protein skimmer so that all the gas bubbles are passing out the top of the reaction chamber, and not escaping into your sump.



  10. avatar

    Hi – I know it’s been a while since any comments on this post, but I am a graduate student working on a lab project and I need to find a way to inject ozone into my old Marineland 100 gallon freshwater recirculating tank.

    I have an air dryer, ozone generator+controller, ORP electrode…however, I do not have a protein skimmer or reaction chamber of any sort. Is there any way I can bubble ozone through my existing system (in the sump), if I am using both mechanical and carbon filtration already??

    If not, do you have any advice on what type of protein skimmer I should use to react the ozone? I am guessing I should look for a skimmer that has an air vent I can cover with activated carbon so I don’t poison the place with ozone…?

    Thanks for the fantastic article — any help would be appreciated! I am very much a novice at setting up aquaria.


  11. avatar

    The best option for your situation is to use an in-sump type protein skimmer as an ozone reaction chamber. Connect the Output of the Ozone generator to the air intake of the skimmer with ozone safe tubing, and let it draw the ozone through the system. I would not recomend using an air bubbler, that is not going to be efficient, and will waste most of the ozone being produced. If you are using a hobbyist type aquarium ozone generator, residual ozone should not be an issue, unless you are in a small confined space. Ozone breaks down very quickly in water, if you already have carbon filtration in place, then you should be fine.

    Thanks for the question,


  12. avatar

    Great article, my question is similar to Anna´s one, I am planning a freshwater closed system (mostly for tetras) for about 3 tanks, in total the system will be around 200 gallons, these 3 tanks with sump, biotowers and the rest, I was thinking in add UV lamp at the end but UV radiation is not enough to control some possible diseases like White Spot.
    I wonder if Ozone can also destoy that kind of possible parasites too?
    I was thinking in the last part of the sump put the Ozone (using small ozone reactor) and after the time of contact (I would apreciate you tell me how long this time need to be) pass the water to other container and before pump it back to the system use a lot of air bubbles to remove any remaining O3.
    For this size of system, what size and kind of O3 reactor would you recomend and what is the dosage?

    Waiting your comments


  13. avatar

    Hello Dave
    This article is extremely helpful. Thank you. I am in the process of planning a wild heckel discus biotope aquarium. It is going to be approximately 700 litres. I don’t have a sump. I have two large eheim canisters one of which is a wet and dry type. I will drill the bottom of the tank and run my canister filters in a closed loop type system. I had initially thought of adding ansurface skimmer fed canister with the chemical media known as Purigen for the dissolved organics plus a uv steriliser unit for getting rid of the unwanted nasties. I also thought of using an oxidator for achieving higher ORP values. Oxidator was relatively popular in the eighties. It works by converting liquid hidrogen peroxide into a steady steam of pure oxygen. Lately, however, I have been increasingly veering towards the idea of using ozone instead. Reading your article made me more enthusiastic about the idea. Can I use ozone in a closed loop freshwater system without a sump? I thought of getting a hobby type ozonizer and using it in conjunction with a specially manufactured fresh water ozone reactor fed by prefiltered water from the surface skimmer. Does this all sound feasible to you? Could I get away with checking the ORP of the tank from time to time as opposed
    To monitoring it constantly? And lastly,
    would I be taking any significant risks
    If I was to allow the water that comes out of the ozone reactor chamber go straight back into the tank whithout letting it past through an additional canister cantaining activated carbon? Would the

  14. avatar

    Sorry, i messed it up… In my last point I was trying to ask about not using activated carbon on the water entering back into the tank
    as this would need to be regularly replaced which I could do without unless I have to. I hope this is not too longwinded. thanks.

  15. avatar

    Tolga, what you are proposing sounds feasable, you can use an inline ozone reactor for your freshwater aquarium. I would definately reccomend that you somehow incorporate a carbon filter inline after the ozone reactor. You do not want free ozone in your display, it can be very damaging to animals in your tank. Running ozone in a closed system is much more risky, than running it in a skimmer in an open sump, which gives any risidual ozone a chance to vent off, before being returned to the aquarium.

  16. avatar

    Hello Dave, thank you very much for your reply and for sharing all this with us. I wanted to ask you about the carbon reactor as it is clear from your answer that i am going to have use one on my system. How do you monitor the effectiveness of the carbon without the risk of letting ozone seep into the water column? Presumably, if the carbon reactor contains enough activated carbon for the job, then it should work and everything will be alright. But after a while, this carbon may become exhausted which means that certain quantity of ozone may seep back into the system endangering the fish. My point is that by the time one realises that this has occurred, it may already be too late, so how does one know at the outset as to how much carbon is needed for the amount of ozone in question and for how long? From what I have read so far, I have gained the impression that there may not be much room for trial and error in dealing with ozone. But I might be wrong as I have not had any experience with any of this. Does the carbon absorb the ozone and retain it permanently in its structure or does it retain it temporarily until ozone transforms itself into something less damaging such as pure oxygen perhaps? Apologies if this all sounds too anal, but I am really interested in using ozone in the discus tank I am intending to set up very soon and I haven’t used activated carbon before so Im not familiar with its possibilities. Also, I have heard that ozone use in aquariums can sometimes lead to the reduction nitrites. It has even been claimed that nitrites can be eliminated completely from the biological cycle or they do not form at all. If that is the case, could this not lead to a dramatic reduction if not total elimination of nitrates? I’m really not sure about this, but I would have thought that Nitrates being the end product of biological nitrification process, would seize to exist in the absence of any nitrites? That is, if there are no other sources such as tap water which could account for their presence in the system. This latter point is pure speculation, so feel free to ignore it but the point about the carbon is something that is bothering me and I’l be grateful if you could shed some light on this. Cheers. Tolga

  17. avatar

    I purchased an ozone air generator recently and upon applying into the two fish tanks, the water in the fish tank was clearer and the fish that was suffering from a bacteria infection on the eye recovered after 2 days. The machine I bought had an in-built timer. By the way, the stale smell was also removed.

    Now, I am a believer in the Ozone machine.

  18. avatar

    Hey guys, I appreciate all the technical appliances you’re all using however, I first applied an ozone machine in a tank that I was keeping threadfin shad that I bought from a fish farm. I had a tank of about 10,000 shad for my trophy fishing pond as a sure fire bait. After day after day of scooping 30-50 dead shad out of the tank, I happened to find an ozone machine that I had acquired from my OCD grandmother and read on the side of my ozone machine that it kills viruses, molds, cysts, bacteria, and chemical contaminants. Well every other fish that was dead and scooped out had weird infections or growths on them and I figured it wouldn’t hurt to try, this was in 2004. So I put a diffuser on the end of the tube which expelled the ozone, attached a suction cup to it and put it in the tank. The next day I scooped out 5 dead fish, the day after that, the water was so clear I couldn’t believe it and oh yeah I didn’t have to scoop out any dead shad. The ozone machine has a timer on the side which allows you to control the time on in 15 minute increments. I was running it for 15 minutes every hour. I didn’t have a protein skimmer, or fancy filtration systems, I had one aquarium filter on it and an ozone machine. Since then, I have connected this machine to all my tanks which house freshwater piranhas, stingrays, barracudas, puffers, and arowanas. The ozone was diffused directly into the tank with a stone diffuser; it looks just like an aerator. I have sold arowanas back to pet stores for ridiculous amounts of money because the water I can maintain them in and the food I feed them is of the highest quality. These arowanas start to turn red in color and people in the U.S. go crazy about this because it costs a lot of money to get a red arowana. I have never measured the concentration of ozone in my tanks or killed my fish or plants in the tanks due to ozone exposure. You can spend as much money as you want on your aquariums but I don’t know if it’s necessary.

  19. avatar

    Hai pg94, what is the output of your ozonizer? 300mg/hour?

  20. avatar

    do you have an item number?

  21. avatar

    My 1019 litre fresh water tank has a sump tank with rock and bio balls. I want to dispense ozone through a large air stone into the over flow stand pipe in the corner box section of the aquarium. The water having been subjected to ozone flows down the pipe into the sump making its way through the various sections before being pumped back up into the aquarium. Is this ok ? Please answer to my email address. Trevor .

  22. avatar

    I would not reccomend using ozone in this manner, there are a couple of potential problems. The overflow standpipe is not going to provide proper contact time with the passing water and ozone. Much of the ozone would most likely just exit the standpipe in the room, which is not good. Any ozone that was able to disolve into the passing water, is going to go strait into your biological filter, which is not good either, it will potentially wipe out your nitrifying bacteria. it would be much safer, and also more productive, to use a protein skimmer, or some other ozone reactor in your sump setup, where the discharge is not going into your main biological filter, and where you can also use some activated carbon if needed.


  23. avatar
    Saltwater Aquarium

    Having an aquarium in the house brings a relaxing feeling especially to the visitors. That’s why we should keep it clean.

  24. avatar

    can ozone be used direct into a marine aquarium,please email your answer to xxxxxxxxxx@xxxxxxxxx.com

  25. avatar

    Ozone should not be used directly in the aquarium, this should never be done. The strong oxidizing action of ozone is damaging to any organic material, which includes the delicate tissues of your aquariums livestock, it can injure or even kill your fish if exposed. You should only use ozone in an external reactor or protein skimmer, ideally in a remote sump or reservoir. This will safely expose the passing water to the gas, but will not allow ozone gas to mix into your display aquarium.

  26. avatar

    I have 200 liters of freshwater tank aquarium connected with BOYU external canister filter with ceramic rings and activated carbon filter media. I would like to add Ozonizer to remove the color of the water and other dissolved impurities from the water. Can you please recommend?…


  27. avatar

    can i ozonize my aquarium with fish and shrimps inside the fish tank or do i ned to remove them first?

  28. avatar

    the ozone is generated in a reactor, the ilvestock should not be directly exposed to the ozone.

  29. avatar
    Kane Chantal Dickson


  30. avatar

    Hi Dave,
    We live on the Cape Verde Islands, have just made a 3000 lit, 800 gal reef aquarium, have skimmers, filters all the lightening and a 55watt UV-C lamp, we also pump water with a timer every 4 hours for 15 min direct from the ocean. The fish we catch local and everything was fine for several days untill they got protozoans, white spot disease, and start to die mostly all of them.
    I am thinking in purchasing a Aqua medic ozonizer 300, will that resolve the problem for the protozoans .
    Thank you for you attention,

  31. avatar

    Gerald, That is an interesting setup you have there. Use of an Ozone unit is very effective at improving water quality, but has limited ability to affect the treatment of parasites like protozoans, since only the water that comes in direct contact with the ozone has the chance to be sterilized. I am curious about your setup, if you have a complete filtration system, why do you need to run water from the ocean so often? This could potentially be the source of your problem, if the temperature or salinity of the incoming water differs from that of your tank, you could be causing quite a bit of stress to the fish in your aquarium with the fluctuations. You also run the risk of introducing unwanted pathogens with water direct from the ocean. You may want to consider staging the incoming water in a reservoir, and making sure of the temperature and chemistry before using it in your aquarium. Treating incoming water from the ocean with ozone would also help limit the unwanted introduction of pathogens.

  32. avatar

    Running ozone directly into your aquarium is not recommended, it is very risky. At very low concentrations you may get away with it, but you are gambling. Ozone oxidizes (destroys) organic material on contact, any organic material. Fish are obviously organic material, and their gill tissue is very sensitive, and can be damaged from ozone exposure. Exposure to low doses of Ozone may not result in visible damage, but it is certainly irritating to the fish. High doses of ozone will damage fishes gills severely, and will be lethal.

  33. avatar

    Dave, thanks flor the article! I was hoping to startnusing ozone in my 750 ltr aquarium.

    I saw your stats and had some questions:

    1) the orp readings in my tank aré currently 490, and i have not added any ozone yet. Can that be right? Or do yo think the meter is off? The water is far from clear….

    2) I built a PVC reactor for CO2. Can I use the same reactor? If not what’s hardware store material can be used? Can I inject CO2 and O3 into the same reactor?

    Manu thanks for your help, Nicholas

  34. avatar

    Nicholas, 490 seems unrealistic, I would calibrate your ORP probe if possible, and check again. I usually find the ORP readings in the 200-300 range without ozone, or lower in heavily stocked aquariums. PVC should be OK for ozone use, just make sure any other tubing or connectors are compatible. I would not recommend mixing gases in the same reactor, not sure what would result from this.

  35. avatar

    Dave… Many thanks for your response. I finally got around to test it with an ORP solution and to my (enourmous) surprise the measurment was spot on the label (measurment of 200).

    Of course this is before adding any ozone.

    If I have these kind of readings does it make sense to add ozone?

  36. avatar

    Nicholas, I am not sure why your aquarium water ORP is testing so high, there must be something affecting the probe in your aquarium, if it reads correctly in calibration solution. I would suggest contacting the manufacturer of your ORP meter/controller, and see if they can provide any further insight into what could be causing such high readings in you tank water.

  37. avatar

    Hi, I have a 6000L freshwater pond with about a dozen 6 inch long fish. I have a bad water borne green/brown algae problem that is intractable.
    I have seen a small sand filter with an ozone producer attached that has a flow rate of 4500L per hour and produces 150mg of ozone per hour. It is actually intended for spa pool use I believe.
    Will this harm my fish and what is the best way to reintroduce the water to the pond that might reduce any leftover ozone if there is any? Would it all have broken down by the time it gets back into the pond?
    As I see it the sand will filter out most particles but algae might still pass through but would be killed by the ozone.
    Is this correct?

  38. avatar

    Rob, I am not familiar with the type of filter you are describing, not sure what the Ozone injection system looks like. Depending on the contact time, and ability to react, it is hard to say what the potential for residual ozone would be. That is not a very big ozone unit, so risk is probably not too high in a pond. Yes the ozone should be treating the water post sand filter, this will help control algae and oxidize organic material that can discolor water. You can also run the water from the filter through activated carbon to remove residual ozone.

  39. avatar

    Hi Dave,

    We have a set up with 8000 gal.of water, recirculating system,we are installing ozone for help with water quality,and bacterial issues. We don’t have the orp meter. We do have the Hach accuvac ozone test kit,which will read off the Hach machine,so when using this it is measured differently than referenced amounts from the ORP meter, are you familiar with this testing kit?


  40. avatar

    Jessica, Typically using a test kit for measuring actual Ozone concentration is used in waste water treatment or other industrial settings where ozone is being used in high doses for disinfection. It can also be used for measuring residual ozone in aquariums or other recirculating systems where live animals are being kept, because of the risks of ozone exposure to any inhabitants. ORP readings are giving you a measure of water quality, in terms of dissolved organic waste, which is oxidized buy the ozone, and the correlation between ORP and dissolved oxygen levels. So depending on what your 8000 gal recirculating system is being used for, use of an ORP meter would also be a good idea. Ozone breaks down very quickly, so if you are using an efficient reactor to expose the water to ozone, and the system is testing free from residual ozone, you should be safe.

  41. avatar

    dave, i bought a ozonizer air pump. it puts out, without a dryer. 100mg an hour, with a dryer 200mg. with it i recieved air line, and two stones. i placed the stone in my aquarium one hour, and the water became very clear. i only need to run it up to one hour. i do not have a skimmer, it is a 55 gallon tank. the few fish i have are fine. is this a ok way to use a ozonizer air pump ? ( rmartelli1234@gmail.com ) thanks.

  42. avatar

    dave, another question, would it be safer to put the ozone stone in my outside filter box, with the lid off, that way if there are ozone gases, they would excape out ot the outside filter box ? is this better, then to put the defuser in the tank its self ?

  43. avatar

    hi again dave, i don’t see my. first question on the list, so i’ll ask again. i have a ozonizer. it puts out with out a dryer, 100mg, with a dryer 200 mg. i placed it in my 55 gallon tank, with in one hour, my tank was beautiful. so i only use it as needed, once every couple weeks for one hour. the fish seem fine ? would i be better, to put the defuser in my outside filter box, with the lid off, for gases to excape ? (rmartelli1234@gmail ) thanks.

  44. avatar

    You should not run ozone into your aquarium with airstones, this is very dangerous to your fish, direct contact with Ozone will cause gill damage. You really should use some sort of reactor, like a protein skimmer, or ozone reactor to safely expose your water, without the risk of residual ozone for your fish. Using it in your outside box would be safer, but is not going to be very efficient, and would still risk residual ozone in your display.

  45. avatar

    HI ALL ! i have had a ozone generator about a year now, good devjce. it puts out 100 mg, small i guess. i do not put the stone in my tanks. i have along with canisters, out side filters, so, i put the stone in the outside filter. my fish are not subjected to the ozone at all, i think. all the gases go out of the filter box. stinky ! i leave it run for eight hours on each tank once every two weeks, just to keep things clean, works very good. all my weekly checks are great, fish are well. fresh water, and salt. 25 percent water changes, every two weeks. a piece of cake. SO FAR. the smell, is stinky, we have to open the windows, and turn a fan on, to blow it out. but we can live with it. hope the birds don’t die, (:-) later, CHOW !

  46. avatar

    I just purchased an ozone generator and ORP contolller on the advice of a nieghbor with extensive saltwater aquarium experience. I have 90 and 125 gal FOWL uniquariums with biological filtration and reef octopus skimmers You suggest attaching the ozone generator to the skimmer inlet. As the octopus skimmers are plumbed with plastic pipe I am not sure how I could attach the ozone generator to the system. Would attaching it to the air bleed valve work? Alternatively could I just place an air stone stone attached to the generator outlet in the back chamber next to the skimmer? I am also concerned about the effect of the ozone on the beneficial bacteria on the bioballs in my filtration system.

  47. avatar

    Trent, If I understand your question, yes, you should attach the Ozone generator to the air inlet tube to the protein skimmer. This will allow the skimmer to draw air through the Ozone unit. I would not recommend running ozone into the filter chamber with airstones, you will definitely put your biological filter at risk from free ozone. The benefit of using a skimmer or reactor, is that it allows the ozone to contact your water, without allowing ozone to escape into the rest of the system. Free ozone is damaging to any organic material, including your livestock and beneficial bacteria.

  48. avatar

    I use and ozone generator to clean veggies and make ozone products at home. One can run the outlet into a glass of water for 5 mins and drink the water (for humans) I want to know if I am able to put this filtered and ozonated water into my goldfish bowl in lieu of oxygen tablets, or if I can use both?

    I have no way of mearuring how much ozone is in the water, I just know that 5 minutes of pumping ozone through a revulare 250ml glass of water is the safe dosage for people. I think my machine has an output of 1000ppm.

  49. avatar

    In general, my response to questions about unorthodox use of Ozone in aquariums is to do so at your own risk. However, what you are proposing to do should be safe for your goldfish bowl, as long as you let the ozonated water sit out in the open for a little while first. Ozone breaks down very quickly, as it is very unstable, it is going to react with any organic material, or simply break down into oxygen within a few minutes. If you give it at least 30 min to rest after ozone, then there should be no residual ozone left in the water.

    You should not have to use oxygen tablets in a goldfish bowl, keeping the bowl clean, and water changes with filtered water should be sufficient.

  50. avatar

    i have a small sea water clone fish hatchery with RAS. i am using the ozone generator to 500 L tank. this will be pumped to fiber tanks. suggest me how much ozone need to be mixed

  51. avatar

    Hello Sesh, I would recommend reading through the “How much ozone needs to be used, and is it safe for aquarium inhabitants” section of this blog for details on the concentration and dosage rate that is recommended.

  52. avatar


    Does ozone react with phosphates in a marine tank? I am having 2 tanks with 24000 Litres of seawater.

  53. avatar

    Hello Ali, Ozone wouldn’t have any direct impact on Phosphate levels.

  54. avatar

    Hi all
    Using ozone solve the problem of ammonia in fish tank but the question, is it harmful to the fish in long scale?

  55. avatar

    Hello Mohamed, Ozone does not appear to have any longterm side effects on aquariums when used at a proper concentration and not used in conjunction with medications like Copper that can have harmful side effects when combined.

  56. avatar

    Is there any other way you can use ozone without a protein skimmer
    I have a freshwater tank size 30 gallons

  57. avatar

    Hello Vincent, Yes, you would need an Ozone Regulator and ORP Monitor as described in this article. Protein Skimmers cannot be used on freshwater tanks.

About Dave Acland

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After graduating from Coastal Carolina University with a BS in Marine Science in 1996, I started my professional career in 1997 as an aquarist at Ripley’s Aquarium in Myrtle Beach, SC. This was an amazing experience, in which I gained invaluable hands on training in exhibit design and construction, as well as husbandry skills for a wide range of animals. In 2000 I started working at That Fish Place as one of the staff Marine Biologists, with the responsibility of maintaining one of the largest retail fish holding systems in the world. I presently hold the position of Director of Aquatic Science, where I oversee the operation of our 35,000 gallon retail aquarium systems, and provide technical support for our mail-order and retail store customer service staff. As an aquatic product specialist, I also provide support for our purchasing and marketing departments, as well as contribute web content and analysis. As a Hobbyist I acquired my love of aquariums from my father who was keeping a large aquarium in early 70’s, and set up my first aquarium when I was 12 years old. I have now been keeping aquariums for over 35 years, and through this time have kept more aquariums and types of fish than I can remember. I set up my first Saltwater aquarium in 1992, which led me down the path I still follow today.