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Why Is My Chlorine Not Working?

Why is my chlorine not working?
Why is my chlorine not working? If you are a frustrated swimming pool owner trying to figure out why you are having issues with your water quality then this article will help you to understand some of the limitations of chlorine and the reasons why yours might not be working as well as it should. First, you should realize that there are in fact a few different situations that you can find yourself in where you have chlorine but it is just not able to do the job you expect it to do. You can also get into a situation where you keep adding chlorine to the water but it is either gone by the next morning, or just not improving the water like it should.


Water quality, testing and balancing for swimming pools is not rocket science and in the vast majority of cases establishing and maintaining your free chlorine, total alkalinity, pH, calcium hardness and cyanuric acid levels is all you need to do to keep your water clear and well balanced (filtering also). Problems with one of these values is enough to cause green water or cloudy water and most water quality problems will be fixed by checking and adjusting these basic values back into the normal range. However there are also times where these basic water chemistry values will not be enough on their own and you need to look deeper to find the cause for your water quality problems.






High pH levels - Something that pool owners do not appreciate is that the pH of the water has a huge impact on how well your chlorine is able to function. The ideal pH range for chlorine is actually much lower than any level you would ever want to bathe in. The pH that we keep pool water to be comfortable for people, 7.4 to 7.6 is actually on the very upper end of the pH range that chlorine will function in. By the time you hit a pH of 8.0 (which is 10 times more alkaline than a pH of 7.0) the chlorine is almost completely inactive in the water. You can measure the water and you can see a free chlorine level above zero parts per million, however the water is still cloudy or green.


Salt water pools in particular struggle with chronic high pH levels due to the type of chlorine generated by electrolysis cells having a very high pH. If your pH is over 8.0 then this is the reason that your chlorine is not able to function in the water properly. It might be helpful to go back to basics and review the pool and spa water chemistry lesson to make sure you have your order of operations right for your chemical corrections. You can also review this article about salt water pool maintenance to learn more about high pH in salt water pools and what you can do to mitigate this issue.



Pool stabilizer - Pool stabilizer, water conditioner or CYA (cyanuric acid) are all different ways of saying the same thing. Without CYA chlorine is "unstable" which means that it degrades quickly when exposed to UV light, like from the sun. No matter how much chlorine you have in your pool water, without any CYA your chlorine levels would reduce by half every hour that the pool is in the sun. At 30 to 50 ppm CYA provides chlorine protection against the damaging UV rays which help you to maintain a free chlorine residual in your pool at all times. However when the CYA level rises above 80 to 100 ppm you will enter a chlorine lock situation where you have a measurable chlorine level, but it is simply not able to effectively kill bacteria and organic contaminants.


This is one of the most common problems that new pool owners will encounter with their chlorine as many people do not realize that stabilized chlorine, like dichlor and trichlor, have high CYA levels and every time you add one of these to your pool you increase the chlorine level, but you also increase the CYA level. If you let the CYA level rise too much then your chlorine becomes ineffective. In theory you can maintain CYA levels of up to 150 ppm however this would require that you also increase the free chlorine level to be 5% of the CYA value (7.5 in this case) in order to have the chlorine still kill bacteria and organic growth. Most residential pools do not operate at free chlorine levels so high, and so the traditional solution to high CYA applies, which is partial draining and refilling with fresh source water that does not contain cynauric acid. Recently there has been a new enzyme product that might have the ability to reduce CYA levels without the need to drain and fill however the feedback from this product has indicated that it is minimally effective, and most pool technicians and pool owners still rely on partial drain and refilling to keep CYA levels in the 30 to 50 ppm range where they should be. For more information you can read this article on pool stabilizer.


High phosphate levels - Phosphates are like a super food for algae and when phosphate levels in your pool climb too high you will have trouble keeping your water clear. Maintaining free chlorine levels with elevated phosphate levels is difficult but the real problems start if your free chlorine level drops all of the way to zero. Now you will develop a reserve of organic matter growth and any chlorine that you add will need to kill everything within the water before you will be able to start developing a chlorine residual. This means that you can end up adding chlorine every day to the pool and by the next morning there is no measurable free chlorine left in the water as it has all been consumed trying to battle the algae and organic matter growth which is being accelerated by the unlimited food supply.


Phosphates are found in soaps and detergents, rural water supplies, farm runoff and fertilizers. We measure phosphates in pools in parts per billion as they are significant in even very tiny quantities. Over 500 ppb you will notice you use more chlorine than you used to, and at 1000 to 2000 ppb you will struggle to keep your pool water clear, and your free chlorine level will be very hard to establish and hold a residual.


Biofilm accumulation - Biofilm is the slimy, sticky gunk that gets stuck to the sides of your pool walls and floor, lives inside your filter, but most especially resides within the plumbing lines for your pool. It is both a food source for bacteria, but also a layer of mechanical protection for bacteria which limits the ability for your chlorine to access and kill it. This biofilm is specifically a problem in swimming pool plumbing because it takes more than chemicals or normal movement of water to fully dislodge and remove it. This is why hot tubs with their hot water bacteria breeding grounds need to have the pipes flushed in between water changes. This pipe flushing process uses a degreasing cleaner which helps to strip biofilms from the inside of your pipes. Pools might not develop as much biofilm as a hot tub will however it is still a problem that can plague certain pools. Since you can not see the inside of your plumbing lines you will probably not see the biofilm directly, but instead the symptom of biofilm which is a difficulty in establishing and holding a residual free chlorine value in the water. A pipe flush is not practical for most pools since you do not actually drain and refill pools very often. In fact with many pool types draining it (or draining it improperly) can result in damage anywhere from minor to major. Since you need to remove the water after pipe flushing this is not an ideal way to handle biofilm accumulation in a swimming pool. Instead if you believe that you have an issue with a persistent biofilm you should consider using a bio film inhibitor product like Aquafinesse. These products help to break down existing biofilm and prevent new biofilm from forming and attaching to the inside of your pipes.


These are the most common chemistry related reasons that you could be experiencing problems with your chlorine and the quality of your pool water. It is definitely worth mentioning that filtration is also very important to the quality of your water and your ability to hold and maintain a free chlorine value. You should be filtering your pool volume three times every 24 hours as the minimum value, which most pool owners do not, as this is a chemical free way to reduce on the contaminants in your water. Every piece of organic debris and bacteria that is physically removed by the filter is one less that your chlorine needs to deal with. If you have leaves floating in your pool or sunken to the pool floor these must be completely removed or you will struggle to maintain your chlorine levels. Skim, brush and vacuum your pool regularly, filter your water volume three times daily, and monitor the chemical levels described above to resolve any problems you have with green water or your chlorine not being effective enough.


Pool chemistry crash course

What is pool stabilizer?

How to get a pool professional to actually return your phone call

Why is pool equipment so cheap online?

How to fix brown pool water

How to make your pool equipment last as long as possible

Essential safety gear that every swimming pool should have




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