Firstly 'and to save me a considerable amount of babbling' I'll offer this link as a pre-curser to covering its connections with reef aquaria. Its a bit in-depth, but it does give you a good foundation of understanding as far your future choices go in relation to its use.

Ozone

So taking the relevant info from that link, we now understand that because of its highly volatile (if short lived) nature, Ozone (O3) is a supreme oxidizer of any organic matter it comes into contact with, and a very good way of sterilizing our water to rid it of possible pathogens, If used in high enough doses.

O3 went through a bit of a surgence within the aquatic hobby way back in the early 90's but then sort of 'died back' as medical research into its real effects became public and people became allot more cautious of the possible dangerous effects of its misuse or overdosing. These concerns are still very prevalent today and should not be under estimated to any degree, so be warned. Misuse of O3 is very damaging, to not only your stock, but also you, and your family.

Doom and gloom aside, does O3 have a place in modern reef keeping?, personally I think 'yes' , but only if you understand its true purpose, uses and dangers.

So  what does it do, and how do you get it in there.?

Well a typical Ozone unit, is a small box of tricks that basically enables you to pump or suck air through it. The air passes between two closely spaced metal surfaces, an electrical charge is pushed through which causes arcing (like miniature lightning.)  and the offshoot, is the generation of free O3 gas. units come in a variety of output ratings. 25mg / 50mg /100mg / and 200mg/ltr. Generally you will attach an Ozone unit to the air feed line of a protein skimmers venturi inlet, so that air is drawn through the Ozone unit before it enters the skimmer. This is considered today, to be by far the best, and safest way of using 03. The very nature of a protein skimmer means that this is the ideal location to mix the highly volatile O3 molecules with normal atmospheric oxygen, with the aim of pulling out, or in the case of O3, virtually  'burning'  harmful organics down through the stages of  ammonia and nitrite down to the least harmful nitrate. As this burning or 'reduction' happens, the amount of 03 is reduced before escaping through the neck of the skimmer. Ozone should never be added via an air stone inside the sump, as the gas isn't burnt off effectively and it may find its way into the main display area resulting in severe damage to stock, especially the gills of fish which it will burn on contact. more importantly, it enables free Ozone gas to bubble off into the atmosphere around your sump and into the room you are in...( Again...Ozone is extremely dangerous at elevated levels)

Ozone will also degrade many forms of plastic and rubber . Any skimmer used should also be compatible. (you should check this with your skimmer manufacturer) likewise, any airlines used should be made from silicone.

Ozone's most common use though, is for the breakdown of tarpines and other dyes that discolour your water as it ages (yellowing). Seeing as little uses these organics, its widely accepted that only the use of Carbon, water changes or Ozone will effectively keep your tank clear over the long term. This is especially prevalent to SPS keepers, as discoloured water both limits the amount of light hitting the corals, and alters the spectrum as it passes through it.  This results in loss of colour / pigment or shifts in colour towards brown.

There are a few other incidental offshoots from the use of Ozone that involve certain metals etc, but these are by and large still very much in the grey area, and as of this time, no official detrimental consequences have been proven to any degree.

How Much should I dose

Well that is the ten million dollar question.....So first I'll cover how you control the dose..

Method 1: Manual control.

This is where you use the adjustment dial on the front of the unit to dial it down or up in terms of its output. many people (myself included)  also run the unit on a timer to control addition to set periods.

Method 2:

This where the unit is connected to an ORP/Redox monitor and controller. The set range on the monitor, controls the addition of 03.

As an experienced reefer who constantly checks my systems and has a good understanding of the process at hand, and for reasons I'll explain later. I'm happy to use the manual method....For those less experienced I would fully recommend the use of an ORP/Redox controller as a safety barrier if nothing else. Even then, there are a few issues with this method which is why I consider it such a confusing issue.

About 'ORP' or 'Oxygen Reduction Potential' / REDOX.

This is a measure of the waters overall condition in relation to its balance between two major groups of molecules. Its a very very complex subject, suffice to say that the easiest way to describe it is to think of a playing field, where you have a team of good guys, and a team of bad guys. The good team are the oxidisers who keep the water healthy and help break down waste. the bad team are the reducers. i.e. a group that specifically deplete the oxidisers and reduce the waters overall chemical stability. (that's the very very dirty version). REDOX 'as we see it', is a reading that tells us what the state of play is...Now, surprisingly, we actually don't want either side to win, we want a constant and ongoing draw. If either side were to win our stock would either be poisoned via increasing levels of toxins, or be oxidised (dissolved and burnt). so we try to keep a balance.

In terms of what the readings mean,  If it has a high Redox reading in the ranges 350-450mv then it is widely accepted that conditions are good and the game is an ongoing  draw. If it has a low reading i.e. sub 250mv  then it is considered that the reducers are winning, if its higher than 450mv then the oxidisers are winning. To put it into real world perspective. A reading of 650mv would see most life killed/oxidised within the water sample in just a few seconds, That includes bacteria which is why ozone  is used in commercial water purification.

 Ozone, as already stated is an oxidiser much like normal oxygen, but on steroids...There are other molecules just like Ozone that are advanced oxidisers as well, and its their relative concentration in comparison to the reducers that determines whether the Redox rises or falls.

So simply put, The addition of Ozone increases the concentration of Oxidising molecules within the system to boost the systems ability to hold the reducers/toxins at bay. Add too much ozone and your in danger of oxidising your livestock, which is where the Redox controller comes in. By setting the controller to cut in at a low level and off at a high level we are able to dose ozone safely in the knowledge that we are not over dosing our tank.

Note I say 'not over dosing'...The common misconception with both REDOX control 'and Ozone for that matter' is that its widely used to 'boost' Redox 'up' to that magical 350mv/450mv range....the problem with this, is that every tank is different and there's no 'definitive' setting that is actually 'ideal' for 'all' systems. the reasons for this are very simple but largely impossible to control. To add further confusion. As Redox rises, pH falls. this is confusing in as much that we widely consider pH as a good indicator of tank health and overall water conditions. I.e. a low pH is indicative of high organics, struggling filtration or poor chemistry (low Alkalinity) and a high pH is considered an indicator of good conditions....so you see, its not all plain sailing as far as using one single parameter as an indicator of tank health.

The Problem with REDOX....As a measure of system condition.

Many people struggle with Redox for one simple reason. They don't understand just how sensitive that reading is to even minor changes within the system, both temporarily and permanently. Even something as simple as putting your arm in the tank to move a coral can dramatically swing an ORP reading by nearly 50 points, so can a fish that has had a heavy feed that's and has taken a poo. likewise RO addition, food, both solid, frozen and liquid, additives, indeed absolutely anything you add to your system will usually upset your reading for a varying degree of time because it chemically changes the balance of oxidisers and reducers for a period of time. Its only 'long' term problems that show up as a persistently depleted Redox reading, or a sudden massively depleted reading that may indicate the death of a major livestock item. From the Ozone users point of view this is very important, because if you have your monitor rigged to 'boost and hold' Redox levels within a range, you'll constantly be dosing Ozone every five minuets and every time you do anything that temporarily depletes that Redox value.  It consequently bounces around even more than if you'd left it alone to do its own thing.. In simple terms. using Ozone to hold Redox in place, is like trying to play a classical piece of piano correctly, whilst a hundred other people are using the same piano..... at the same time...all playing different songs......There's just too much interference to get a definite feel of what sounds right or wrong.

This is where logic should come in to play...Simply put, how many systems crash because they are neither monitored for Redox, nor have Ozone addition ?.......... The simple answer is 'none'..

Never forget, that in a well run and sensibly stocked aquarium with regular water changes, the chances of crashing the Redox reading are virtually 'NIL' unless 'you' do something really daft, or completely miss a large dead animal that pollutes the tank. If it 'were' possible, we would have all been using ORP monitors years ago and they would be considered on a par with hydrometers.. as it is, Redox/ORP monitoring should be kept to what it is, simply a 'rough' indicator of whether the tank is ok with regard to its oxidising potential over a period, not at one single point in time (unless alarmingly low).

So, my honest advice, is to use the controller to prevent 'overdosing' of Ozone only. i.e. set your controller to turn off the Ozonizer should levels exceed 450mv at any given point in time. but not have it set to turn the Ozonizer 'on' for any given reason...For that, use a timer..

Ozone...The drawbacks...

Remember what I was saying earlier regarding the efficiency of Ozone to oxidise organic material both living and dead? well this is where we come to questions regarding the usage of Ozone and its drawbacks. As any advanced reef keeper will always attest, what splits a mature system away from an immature one, is the amount of diversity to be seen. Not just in larger life forms, but in micro fauna as well. It is widely accepted that a diverse system has a higher ability to adapt to changing/fluctuating free waste levels, than a barren one. Plus these elevated populations of micro-fauna provide a valuable and natural source of food to the rest of the system helping to build a much better representation of a natural cycle, more akin to real reef, than to a test tube. This is after all, what we are trying to emulate.

Baring this in mind we should consider the fact that any larval life forms, fertilised eggs, or sperm that go through a skimmer utilising Ozone, will invariably be damaged to varying degrees,  dependant on the dosage rate at that time, and the efficiency of the skimmer. Now baring in mind that the highest proportion of spawning/breeding takes place under cover of darkness, I would urge People not to use Ozone during the night time period as it may considerably deplete micro-fauna populations over time through limiting larval spread and fertilisation. This I feel could over the long term hold the system back to a detrimental and possibly dangerous level. It is quite common for many Ozone users to feel the need for ever increasing doses to keep the system stable. Diversity depletion 'could' be a major factor in this as the system needs more and more assistance to deal with unwanted waste levels and pollution, as the critter population decreases. In this respect Ozone 'addiction' is a very real possibility in my opinion, and a situation which I feel I have witnessed on occasions. Typically in these cases, sudden reduction of Ozone addition leads to faltering corals, rapid loss of colour and and an overall downturn in conditions faster than would be expected, compared to a standard system thats had its skimmer turned off for a period of time. This is 'I feel' a good indicator of system addiction.

The second thing to consider is what you are using Ozone for ?... Yes, it 'is' very good at breaking down ammonia to nitrate. but, that's where it stops. It doesn't do the same job as Live Rock, nor a sand bed which takes waste right through the entire nitrogen cycle back to harmless nitrogen gas. For this reason permanent use should be very carefully considered. Remember that bacterial populations and micro-fauna, are in direct proportion to the amount of food available. If you steel that food away, populations decrees and you become more and more reliant on the new 'artificial' method...If that then breaks, it can cause untold problems and a potential disaster as the system battles to look after waste that's got nowhere to be processed. Baring this in mind, I would recommend not running the Ozone all the time, and to keep it in moderation. As an indicator of this imbalance, It is very common that an increase in algal growth rate will be encountered on the glass panels of the aquarium whilst the tank is running Ozone. this is simply because the ambient levels and concentrations of No3 have shifted slightly at a chemical level. It is not uncommon to witness slightly elevated No3 levels when running O3. Not too bad, unless your system doesn't have the de-nitrification capacity to deal with that extra load. A skimmer that is running normally pulls out organics 'before' they get a chance to break down, whereas a skimmer that is running 03, is effectively a super efficient ammonia and nitrite reducer with only the largest organics making it past the O3 to be pulled out by fractionation.

So finally, we come to the nitty gritty. The vast majority of people utilising Ozone are doing so to simply get extremely clear water, and effectively maximise the amount of electricity they are using to light a yellowing tank. how much is required.? well this is where I'll surprise many and go completely 'against manufacturers recommended doses, in that I've found a dose of only 10-20mg/l  for just two hours per day just after lights on is normally 'more' than enough to keep crystal clear water on a heavily stocked 200gall system quite easily.

Just 20mg/l for 2 hours/day is all you need for crystal clear water on a 200 gallon heavily stocked and fed system.

Some people claim that O3 can help control the spread of White spot. I am of the opinion though, that at the dosage required to kill parasites (in excess of 650Mv within the skimmer body for at least 1 minute) means that this is sheer luck, at best, and puts an unnecessary strain on the system as a whole. Personally, I think there are far better ways of solving the initial problem (cause of the infection), rather than using such an aggressive and potentially detrimental method to fight the symptoms. Its like using a sledge hammer to crack a wall nut.

The commonest statement and mistake made by many is  'since adding Ozone my tank is thriving, and looks stunning ' but no explanation is offered beyond that statement. Remember that clear water can be just as deadly as dirty water, and that water clarity bares no relation to what's going on at a biological level over the long term. This where the final warning about O3 comes in.

Taking all the above into account, its easy to see just how much of a 'good job' Ozone does of clearing up a mess, and keeping things in check. But equally that can be the downfall of many, because it is so good at disguising serious problems until the unit fails. at which point the rate of collapse can be quite dramatic and potentially costly. For that reason I would strongly urge people 'NOT' to bolt Ozone units on to new or immature systems until such time as the system has been proven to work at a biological level effectively, and you have developed your reef-keeping skills to the degree that you can hold a reef stable without the assistance of O3. Even then, I would advise the following as a guide to successful and educated use of this substance.

OZONE in Practice. the safe guide.

1. Control initial 'On' times via a simple timer. and set to 2 hours per day just after lights on.

2. Set your Redox controller to monitor and prevent the Redox from going 'above' the 450mv mark, but ignore the fact that your system might be happy running at 300mv as an average..( remember Redox isn't a definitive, its only a guide.) your only interested in stopping an 'overdose' not preventing an 'under dose'.  Recalibrate your probe regularly, and keep it away from other electrical apparatus as they might affect the reading.

3. Start small. 10-20mg/200gall for 2/24  is more than enough for most systems to get pristine water.

4. Place a small bag of carbon over the outlet holes on the top of the skimmer to absorb surplus escaping O3. ( But you probably wont need it at such a low dose)

5. The out flowing water from a skimmer using O3 should never run directly back to the tank. it should always be allowed to dispel excess O3 before coming into contact with your stock. (a net bag of carbon under the outlet can help with this)

6. If you can 'smell' Ozone in the room your tank is in, your overdosing not only your tank, but probably your family as well...Reduce the dose immediately. A faint whiff above the skimmer is normal though, and represents no major health risks as long as you don't play silly beggars and sniff it every 2 minuets.

7. Crystal clear water doesn't mean its healthy. You still need to test.

8. Always remember that O3 should be considered a tweak, to enhance an 'already' functional and well maintained system. It shouldn't control how a system runs by becoming a major player in water quality control.

 Don't become a slave to its charms.

 I hope this topic has been of assistance to you. and many thanks for reading.

Simon.