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In the end, you have a bunch of dead stuff in your pool. Ozone will not only oxidize a lot of it into nothingness, but will microflocculate the rest into filterable lumps. Add to that the fact that it kills most everything and much, much faster than anything else and you have the ultimate system enhancement.
Also consider the various chlorine forms. While the form it takes in a high pH environment will get nuked quite readily by Ozone, at the lower pH you should be running your pool at it is a different story. This is one reason some commercial pools would appear to still have high chlorine consumption. If you don't keep your chemistry in line not much is going to show a vast improvement and I know many pools seem content to keep their chloramines down to .5 or .7 or so, not really a good practice considering they are trying to knock it down from over 1.0 all the time. I am sure Richard can elaborate on all that.
The issues I have seen with Ozone are similar to every other system out there, bad design and lousy maintenance. I think Ozone however is by far the best choice.
As for Ozone staining and damage, combine undersized contact tanks and oversized Ozone systems so you properly eat up your ORP probes constantly. Then override that system to dump tons of Ozone directly through the equipment and into the pool. This results in destroyed equipment and lots of nice staining at the returns as the Ozone oxidizes everything in the area. Its easy!
Though I explained the sources and magnitude of each for chlorine consumption/usage, I didn't explain the various requirements for the level of Free Chlorine (FC) needed. I mentioned about the FC/CYA ratio and have written about that elsewhere since that is related to the active chlorine (hypochlorous acid) concentration, but the amount of active chlorine that is needed varies depending on what you want to do. Algae prevention takes the highest level of active chlorine so that's where the FC/CYA rules come from, but those rules assume you do nothing extra to prevent algae growth.
If one wants to have a lower FC level (actually, an FC/CYA ratio), then one can use an algicide, phosphate remover, borates or copper ions (but be careful of staining) to inhibit algae growth. That will usually let you have a lower active chlorine level, half or perhaps one-third. This does lower the disinfection rate, but most bacteria are very easily killed and in a residential pool the risk for disease is low anyway. An FC/CYA ratio of even 1% will still prevent most uncontrolled bacterial growth, but it does mean that it takes around 10 minutes for a 3-log kill of common fecal bacteria rather than only taking somewhat less than 1 minute for the same level of kill with a 10% FC/CYA ratio. Commercial/public pools should probably not go so low, though the current standards with 1 ppm FC minimum an 100 ppm CYA maximum are that 1% FC/CYA ratio. Specifically, APSP-11 states the following:
I disagree with the above since the few real pool studies are not inconsistent with CYA having an effect, but that bacteria are so easy to kill that they couldn't see it -- that is, they were mostly only seeing whether the active chlorine level was high enough to prevent uncontrolled bacterial growth, not to see if someone with a large bacterial introduction or a viral or protozoan oocyst introduction could transmit disease to another person in such water. Pools are not alternative universes where the laws of chemistry, bacteriology, physics, etc. are suspended. There is more going on, but some studies have used real pool water with the same results of a large CYA effect as seen in buffered distilled water and indirect indicators, such as ORP as shown in the graphs in this post, do track the active chlorine level even in "real pools".
In high bather load pools, you need faster oxidation rates since there is a faster introduction of bather waste so that's another reason for a higher FC/CYA ratio in such pools, though another alternative is to use supplemental oxidation which has the advantage of lessening the amount of disinfection by-products.
For those who want the closest thing to a chlorine-free pool with minimum disinfection by-products, then use 2 ppm FC with 100 ppm CYA which is equivalent to 0.02 ppm FC with no CYA and use a supplemental algicide such as PolyQuat 60 added weekly. If the bather load is higher or this is an indoor pool, then use a supplemental oxidizer such as non-chlorine shock (MPS) or possibly ozone if you get an ozonator that is actually large enough to be effective (or UV, especially for indoor pools). For a hot spa, one can use Nature2 (silver ions) with MPS which is EPA approved as a disinfectant, though realistically one usually needs to use Dichlor once a week to keep the water clear as MPS will not oxidize everything the same as chlorine.
Richard,
Thank you for the explanation. I have a much better understanding of ozone in the residential pool.
Ozone doesn't provide a substantial residual in the water (and adding enough to do so would be too risky to outgas and be potentially harmful) so it doesn't lower the requirement for the chlorine level from a disinfection point of view. It can lower the amount of daily chlorine required (i.e. amount consumed so amount needed to be added) under conditions of higher bather load. Many residential ozone systems for pools are woefully undersized, but a well-designed system can provide benefits. However, it really depends on bather load.
A very clear example of this is with residential spas. There are hundreds of examples I've tracked on a spa forum regarding chlorine usage, ozone vs. no ozone, and bather load. The result is consistent and clear. The ozonators for residential spas are mostly good in that they do produce a measurable difference. If the spa is used frequently (every day or two), then an ozonator lowers total chlorine demand roughly in half for daily spa use. This comes from ozone oxidizing bather waste (mostly urea, I suspect, plus possibly some monochloramine from chlorine combined with ammonia) so that chlorine doesn't have to. However, when a spa is not used very much (say, once a week), then the chlorine demand goes up, roughly doubling. This is probably because ozone can oxidize chlorine to chlorate and may also have the increased aeration force some faster outgassing (though with the spa covered I think the latter is less likely).
So for pools, a higher bather load situation can definitely be helped by using ozone so for commercial/public pools that usually have high bather loads it should cut down chlorine demand just as other supplemental oxidation systems can do such as using non-chlorine shock (MPS) or enzymes. This can also help to reduce the amount of disinfection by-products. However, for residential pools that are outdoors, the largest consumption of chlorine comes from chlorine breakdown from the UV in sunlight, even in pools that are properly stabilized. The amount of chlorine demand from bather load in most residential pools is very low except when one has a large pool party in a smaller pool.
One can use the rough rule-of-thumb for spas to roughly figure out the chlorine demand for pools. In a hot (104ºF) spa without an ozonator, the oxidizer demand for every person-hour of soaking is roughly 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach of 7 teaspoons of non-chlorine shock (43% MPS). This is around 7 ppm FC in 350 gallons. The equivalent in a 10,000 gallon pool would be 0.25 ppm FC and usually the amount of sweat/urine in a cooler pool is around half that of a spa unless there is vigorous continuous exercise (i.e. competitive swimming) so really closer to 0.15 ppm or so (and less in larger pools). Typical chlorine demand in stabilized outdoor pools is around 1.5-2.0 ppm FC per day when there is little or no bather load and when there is sufficient chlorine in the pool to prevent algae growth in nearly all pools without the use of supplements (so having roughly 4 ppm FC with 50 ppm CYA in non-SWG pools or 4 ppm FC with 80 ppm CYA in SWG pools, for example). Also consider the differences in turnover rates between a spa and a pool. The ozonator is only able to oxidize what gets circulated and even then, only the very small part of chlorine demand associated with bather load (or other organics getting into the pool) and does nothing to prevent the chlorine breakdown from the UV in sunlight.
Even with no bather load and with a pool or spa covered, there is chlorine demand from oxidation that is a function of temperature. In hot spas this is usually seen as around a 25% chlorine demand so 1 ppm FC if the target is 4 ppm FC (say, with 30 ppm CYA). In my own 88ºF pool, it's lower where without use and with a mostly opaque electric safety cover it's around 0.7 ppm FC per day and perhaps a 15% daily chlorine demand. Some of this, perhaps around 0.2 ppm per day, is due to chlorine oxidation of CYA while the rest is oxidation of any accumulated organics, of metal, of the pool sweep, and some outgasssing and oxidation of the pool cover itself. At lower temperatures closer to 80ºF, the demand goes down, perhaps to around 0.4 ppm.
From the tens of thousands of pool owners reporting on pool forums, there doesn't seem to be any benefit from those who have ozonators. Given the data above, this is understandable. Bottom line, an ozonator is useful when the bather load is high -- this is usually the case in a residential spa used every day or two and in many commercial/public pools, but is not the case in a residential spa used infrequently or in most residential outdoor pools. There is probably some benefit in indoor pools to reduce chloramines, but UV may be better for this -- too few data points to know in the residential market and for commercial/public pools this argument doesn't seem settled yet as the by-products from each process are different and neither is ideal, though either is much better than not having any supplemental oxidation at all (for high bather-load situations).
There have been a lot of posts on this threaded regarding copper/silver ionizers however I have not seen much information on Ozone. Ozone seems to be the best option in reducing chlorine as it does not have the same staining issues that ionizers tend to have, while still allowing a low chlorine level. Does anyone else have any ozonator experience they can share?
Hi everyone! First post, thought I could share my experiences with the copper/silver ionizers. I sell them, but I will never install one unless the deal is I get to put them on service as well. I no longer sell one and leave a customer to manage it. Thats because from my experience there's a whole plethora of unique problems you WILL come across, and they need specific care and knowledge to prevent them. Also, the average customer has a hard enough time with traditional pool sanitation (which is most likely why they hired me!). That being said, I still advocate the systems because they do save money. I've had varying success keeping the pools clear and chlorine free; it worked to some degree, but the pools must be PERFECT in every other aspect ie filtration, balance, sanitizer load etc. Plus, I question the safety of water with no chlorine. So I do use chlorine, just not NEARLY as much. I shoot for a 0.5 residual, and the water seems to keep better than my regular chlorine pools with a 3 or 4 FC. I also get complimented on how the water feels compared to before the ionizer. So I guess in short, don't be afraid of these systems and don't tout them as a chlorine replacement, but a supplement.
Curtis
For the purposes of humor I was a bit heavy on the sarcasm. I tone it down slightly when discussing the issue with clients. It normally gets a grin, then I can start explaining the various systems we sell.
Non! Chemical free pools don't exist. Realistically if you want to take it to another level water itself is a chemical. Chemical free customers want a vacuum sealed rubbermaid container with no water or air.
Rick Larson said:
Not sarcasm, truth! LOL How many people have called or come in with ear infections and skin rashes from chemical free pools. They have Ion, or UV, or Ozone or ..... some other "system" someone has sold them. They all work great in conjunction with ........... drum roll ........ Chemicals!
Mmmm, maybe snake oil works?
Scott,
Is it just me or does the sarcasm come off as a little thick?
Scott Heusser said:
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