Pool UV Systems
A common theme with pool owners these days is a strong movement away from chlorine and other chemicals traditionally used to maintain safe swimming pool water. Certainly the desire to make your pool as safe as possible is a good thing, but the subject of safe versus unsafe pool water is a very broad technical subject, and one that is quite open to interpretation. I have previously written about chlorine free pools and how the technology is not quite there yet to maintain reliably safe swimming pool water without the aid of any chemicals. Some people claim that they are chlorine free, or chemical free, and yes there are certainly many ways to get close to safe...or safe enough for a backyard residential pool that does not get a lot of use. But would these same people be willing to swim in a pool filled with other people who have known communicable diseases like flesh eating bacteria or MRSA? If they would their bravado could get them killed because the one thing that all chlorine alternatives lack is a powerful residual in the water.
Chlorine is able to hold a residual value in the water, called free chlorine, and this is what would stop you from getting a disease from an infected person who is swimming next to you. This is also what protects you from errant animal feces that can find its way into your pool. One of the only chemical alternatives to chlorine is a modified oxidizer product that can hold a residual however it is not proven effective enough to be approved for commercial pool use, and it can become ineffective over time requiring water changes in the pool. In the world of peripheral equipment that can improve the water treatment for your pool, all lack the same residual property. This means they can be highly effective at killing bacteria and viruses, to the tune of 99.9%, but there is no protection until the infected water has passed through the filtration system which can take many hours per cycle. It is possible that soon technology will have a proven system for making pool water completely safe, including a residual, but that is not certain at this point. The newest technology looks very promising and is just starting to hit the open market very recently. So recently in fact that most people, pool technicians included, don't know what advanced oxidation potential is, or how you can use it on a pool. For more information on this new technology you can read this article on AOP in pools or these AOP system reviews if you want to get one for your pool.
When it comes to designing the system that is the best of both worlds, low chemical exposure with high probability of safety, I have always leaned towards low levels of chlorine combined with germicidal UV systems. It is very possible that AOP systems may be even better, but UV systems are reliably proven to be over 99.9% effective at destroying bacteria and viruses. This is why in places where there is highest risk for infectious contamination, splash pads for children, having chlorine is not enough - UV is recommended at minimum, and enforced as law in many places. The reason why all boils down to one thing. Chlorine is highly effective at being a sanitizer, oxidizer, algicide and holding a residual value in the water, but it does have a weakness. Chlorine is not particularly effective against the cryptosporidium parasite.
Why UV Needs To Be Used With Chlorine
Chlorine is effective at killing almost all bacteria and viruses in your pool water within one minute at a concentration of just a single part per million...except crypto. The cryptosporidium parasite has a tough outer layer which provides protection against chlorine. Chlorine can and still will kill crypto but it needs a lot longer than one minute, and a lot stronger of a concentration that one part per million. This is one of the reasons why super chlorination is important in pools as periodically the chlorine level should be raised to much higher than normal levels for a sustained 24 hour period of time. It requires these higher levels of free chlorine, in excess of 10 parts per million, the better part of a full day to kill crypto with 99.9% effectiveness. This is the primary drawback to chlorine based systems in swimming pools. The CDC reports that cryptosporidium is one of the most common causes of waterborne diseases and exists throughout all regions of the USA and around the world.
One of the biggest concerns with crypto is that most pools are not super chlorinated properly, or regularly, which leaves the door open to getting sick. This is especially true for pools that are used by children, the elderly and people with compromised immune systems. This is why high risk water parks like splash pads are now being required to have supplemental UV systems installed. UV systems might lack the ability to hold a residual value in the water, but they are very effective at destroying cryptosporidium. This is why chlorine and UV systems go so well together and are something that I recommend to any pool owners looking to reduce exposure to chemicals and make the water safer.
When you use UV and chlorine together you get the ability to destroy crypto with 99.9% effectiveness, but you also have a powerful sanitizer reserve in the water for any other contaminants that find their way into your pool. Pools with adequately sized UV systems use dramatically less chlorine overall than pools without a supplemental system. This is because the UV light also destroys other bacteria, viruses and parasites in the water, not just crypto, and so you use less chlorine overall. Less chlorine means lower overall exposure to chlorine, less exposure to chloramines, and less chemical corrections to the total alkalinity and pH of your pool.
UV Lights For Pools
UV lights for pools can be added at any point to a pool system, and they work with all types of swimming pools including fiberglass, vinyl liner or concrete (gunite) pools. UV lights are also compatible with all other forms of pool chemicals and equipment such as salt water pools and chlorine. UV lights are also very easy to install compared to other systems like salt water which can require that you add hundreds of pounds of salt to the pool. A UV system installs into the plumbing system right before the water returns to the pool and usually comes with a cord that you plug in (or larger units are hard wired in place). If you are concerned about reducing your exposure to chemicals, making your pool safe, but spending as little money as possible then buying a UV light is the best option that you have.
Sizing UV Systems - A UV system of any size will reduce the amount of chlorine used in any size of pool, however for maximum effeciency you would calculate the flow rate of your pool system and match this to a suitably sized UV light. So long as the water is clear and free of turbidity then a germicidal UV light will destroy 99.9% of the viruses and bacteria that passes by the light within the flow rate it is designed for. If a UV light can handle 50 GPM of flow rate then this means it can process 3000 gallons of water per hour, or up to 72,000 gallons per day. Ideally you want a UV light which can handle the entire volume of your pool in 8 to 12 hours as this allows for a turnover rate of two to three cycles per day.
Solaxx UV1500A UV Light
Flow rate: 35 GPM
Bulb life: 14,000 hours
Bulb size: 35 Watts
SOLAXX UV3000A UV Light
Flow rate: 70 GPM
Bulb life: 14,000 hours
Bulb size: 50 Watts
Paramount Ultra UV2 Light
Flow rate: 20 (minimum) 80 (maximum) GPM
Bulb life: 13,000 hours
Bulb size: 52 Watts
Ozone is often confused with germicidal UV systems because ozone can also be generated with a light, however ozone and UV are completely different technologies. They both help to reduce chlorine demand in a pool, and they both cost about the same amount of money, however they work very differently. Ozone is an oxidizer, which is no different than other oxidizers in a pool such as chemical oxidizers like potassium monopersulfate. Ozone oxidizes and kills bacteria where germicidal UV light destroys the DNA of bacteria and viruses - not kill. This is a subtle difference as far as the average pool owner is concerned, and both UV systems and ozone systems have their advantages. I tend to prefer UV lights as they are easier to install and have no smell or byproduct where ozone systems produce, well, ozone, and you can smell it. Ozone also can contribute to oxidizing and bleaching some pools. For simplicity, UV systems are superior, but if you would like more information you can also read these pool ozone reviews. If you want the absolute latest and greatest technology for your pool then you can look at these AOP system reviews which combines both ozone and UV together to create something even more powerful at killing bacteria in pool water - hydroxyl radicals.
What is AOP?
Ozone system reviews
Pool chemistry crash course
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