Since the thread Ozone cleaner brought up the topic of ozonators from a manufacturer, I want to analyze some statements made on this website (note that such statements are fairly common to all ozone manufacturers so this is just an example). Let's look at some of these statements individually. Many of them are not outright falsehoods, but when applied to outdoor residential pools they can be misleading.
The main flaw in the above reasoning is the implied assumption that the bather load in residential pools is large enough to have a noticeable amount of chlorine reacting with the organic compounds (and ammonia) mentioned. That is simply not true in most cases. The bather-load from the nitrogenous chemicals in sweat and urine along with chlorine reacting with skin and swimsuits is roughly 4 grams of chlorine (as Cl2) per person-hour. In an 18,000 gallon pool this is only (1000 milligrams/gram) * (4 grams) / (68137 liters) = 0.059 mg/L or ppm. I would not call this consuming a lot of chlorine.Ozone and chlorine differ in how they oxidize other compounds. At pool or spa residual levels, chlorine becomes incorporated into the compound. This chemically alters the compound. In this fashion, chlorine combines with organic compounds in the water. These organic compounds include body oils, suntan lotions, cosmetics, dead algae and bacteria. These reactions consume a lot of chlorine – and chlorine is no longer available to function as a biocide and residual. The altered chlorinated organic compounds (combines) form scum lines and greases that clog filters, (remove) and form layers with calcium carbonated which result in the formation of soft-scale.
As for suntan lotion, it too does not result in a measurable chlorine demand and I speak from personal experience about this since my wife swims almost every day in our pool and uses sunscreen regularly. The cartridge filter is full of such suntan lotion when cleaned once a year (they are oversized filters) and the chlorine demand does not change at all after an entire season of accumulation vs. after cleaning the filter (at least within 0.2 ppm FC per day which is the resolution of the FAS-DPD chlorine test using a 25 ml sample size). Suntan lotion has many compounds, but only some of the FDA allowable active ingredients are nitrogenous compounds with which chlorine will react.
As for the chlorinated organic compounds forming scum lines and greases that clog filters and removing and forming layers with calcium carbonate, not only have we not seen this being reported but I don't see the chemistry that makes this happen. Scum lines are typically from a combination of calcium or magnesium with soap forming calcium or magnesium stearate. In pools saturated with calcium carbonate to protect plaster surfaces one can have calcium carbonate scale, but that does not involve chlorine. "Greases" would be greases without chlorine and chlorinated organics would not become more grease-like.
Again, the amount of chloramines that are formed are a function of bather load and the amount is not "considerable" in a low bather-load pool. Also, with the low active chlorine levels in the Chlorine/CYA Chart, there is less nitrogen trichloride produced. The UV in sunlight also breaks down dichloramine which is a precursor to nitrogen trichloride. Chlorine oxidizes ammonia mostly to nitrogen gas and some nitrate, and very very little nitrogen trichloride when the bather load is low.At operating residual levels, chlorine also combines with nitrogen-containing compounds to form chloramines. Chloramines are less effective biocides than the killing forms of chlorine. Chloramines are responsible for the eye and skin irritations associated with chlorinated water. The formation of chloramines consumes considerable amounts of the free available chlorine. More chlorine needs to be added to establish a sufficient free chlorine residual in the water, a process known as “superchlorination” or “shocking”.
Superchlorination or shocking is not needed if the chlorine level is properly maintained, especially when the bather load is not high. Breakpoint chlorination is continuous. In my own pool, I almost always measure <= 0.2 ppm CC and that is also true for the vast majority of outdoor residential pools that are properly maintained. Furthermore, most of this CC is chlorourea and monochloramine, not dichloramine and nitrogen trichloride. Chlorine reacts very slowly with urea, but ozone also effectively does not react with urea, but ozone does react more with chloroureas so that could be helpful if they built up to high levels, but that doesn't happen in low bather-load pools.
There is a fallacy that just because an oxidation potential is higher, that "ozone is a more powerful oxidizing reagent than chlorine". Oxidation potential is a thermodynamic quantity that says what is possible, not the rate at which it actually happens. Oxygen has an oxidation potential that should be oxidizing the organics in our bodies (or in wood) to carbon dioxide, nitrogen gas and water, but that doesn't happen except at high temperatures (i.e. burning). Whether a reaction actually happens, or happens quickly enough to matter, depends on reaction kinetics which depends on temperature and activation energy, not just on thermodynamics. See Chemistries of Ozone for Municipal Pool and Spa Water Treatment for many such fallacies. It is true that partial oxidation can still be helpful, but ozone does not oxidize that many more compounds than chlorine in pool water. See Use of Ozone in the TreatmentOzone acts as a primary oxidizer, not as a disinfectant or biocide. Disinfection is achieved by maintaining a free available chlorine or bromine residual. Because Ozone is a more powerful oxidizing reagent than chlorine, Ozone reacts with organic or nitrogen containing compounds faster. Ozone does not combine with other compounds; instead, it causes the organic and nitrogen compounds to break apart. The smaller molecules are more water soluble, and some can even gas-off. Amine compounds are altered so that they no longer combine with chlorine. Ozone stops the buildup of chlorinated organic and amine compounds and does not form combines.
of Swimming Pools and Spas (see Tables 9 - 13).
When ozone breaks down, which it does more quickly at higher pH, it breaks down into a variety of oxygen species the most powerful of which are hydroxyl radicals, OH•. The thing is that chlorine also breaks down into hydroxyl radicals from the UV in sunlight. The difference is that with ozone this radical production occurs mostly in the contact chamber (if one is used where ozone can remain in contact with pool water for minutes), whereas with chlorine it occurs throughout the pool water (UV penetrates deeply into water, unlike infrared).
Again, this is simply not true. No weekly or regular superchlorination or shocking is needed in a properly maintained outdoor residential pool. The key is understanding the chlorine/CYA relationship because standard industry recommendations for FC and CYA do not account for the basic science known since at least 1974 as described in this paper. Pools not following the FC/CYA relationship typically have too low an active chlorine level so algae can grow faster than chlorine can kill it. This may not always result in visible algae and may instead result in dull/cloudy water or in a higher chlorine demand. It is in such situations where ozone or any other supplemental systems including algaecides and phosphate removers seem like a miracle, but these extra products or systems wouldn't be needed if the proper FC/CYA levels were maintained in the first place.Without Ozone, the homeowner uses much more chlorine to keep a free available residual and requires “superchlorination” or “shocking” compounds and other specialty chemicals to treat problems caused by pool oxidation by chlorine.
Ozone is very, very useful when the bather-load is higher (many commercial/public pools and spas and high-use residential spas) as it can oxidize the bather waste (and other chemicals) before they build up to high levels, sometimes before chlorine reacts with them while other times afterwards. Ozone is also useful at inactivating the protozoan oocyst Cryptosporidium parvum which is highly chlorine resistant. Ozone also oxidizes bromide to bromine (and some of it to bromate) so is useful in bromine spas.