inPERSPECTIVE / AQUATICS: Get the Most Out of Your Chlorine During a Chlorine Shortage

2020 brought hardships for pools in many capacities. Whether it was closings or having to run at half-capacity, we all saw our bit of heartache. But things got even harder in August 2020 when a fire at a major Trichlor manufacturer drastically reduced the U.S. production of this type of chlorine, commonly used in backyard pools, by 40%. Combine this with the increased demand for chlorine brought on by a surge in home pool builds (up approximately 26%), and a heightened priority for chlorine used in drinking water and wastewater treatment plants, and it's easy to see why the commercial pool market is experiencing the biggest chlorine shortage in decades.

What can pool operators do in a situation like this?



One of the best ways to make the most of the chlorine products that you have on hand is to ensure that you are storing them correctly. Chlorine tablets, granular and liquid bleach all have a shelf life, meaning the effectiveness of these products decreases over time. Storing your chemicals in a cool, dry and well-ventilated area will help lengthen their effectiveness. Ideally, never store any chemicals in direct sunlight. As can be seen in Figure 1, the more concentrated a bleach solution is, the faster it will degrade and lose its chlorine assay. Note the effect that an elevated temperature of 85 °F has on assay. Temperatures closer to room temperature are recommended for your chemicals' shelf-lives.

Chlorine Consumers

What can you do to keep the chlorine you do have in your water stay put longer? Decreasing chlorine demand in water is a good first step! Any contaminants entering a pool will eat up your free chlorine and require you to put more and more in to keep a safe and healthy pool. Contaminants are brought into pool water through a variety of routes:

  • Swimmers who don't shower before getting into the pool. These swimmers bring soap, makeup and even laundry detergent into the water that can dramatically increase chlorine demand. Therefore, showering before entering the pool should be mandatory.
  • Sweaty swimmers! An active swimmer can add anywhere from 0.3 to 2.5 liters of sweat every hour. Multiply that by the number of swimmers in your pool, and that all adds lots of nitrogen compounds that will eat up your chlorine while providing nutrients for algae.
  • Common debris from trees and landscaping runoff can consume chlorine as well. These also bring lots of nitrogen into your pool. Don't wait for chloramines or algae to develop. Shock regularly as it will take more chlorine to fix a problem than to prevent it.
  • Rainwater can bring contaminants into your pool leading to unbalanced water while also diluting your chlorine. If it rains enough, your water level can rise above the pool skimmers, leaving debris on the water's surface as the skimmers can no longer remove material. Rains can bring in phosphates and nitrates, which algae thrive on. Regular shocking during a chlorine shortage is important and will help eliminate contaminants before they cause more problems that require way more chlorine to correct. Additionally, reducing your water level will allow your skimmers to work properly.
  • Got algae? Algae devours free chlorine! Make sure that all of your water return jets are working properly and that you are circulating your water to achieve at least one turnover every six hours. This will help catch more contaminants on the filter to prevent eating up chlorine unnecessarily.

Calibrating Controllers

If you have a larger facility, you probably have controllers that regulate how much chlorine is added to your pool at any given moment. Making sure that the probes used for these controllers are working properly is a huge step toward conserving chlorine. As you perform your routine water balance checks with test kits, compare these results with the readouts on the controllers. If the readings are more than 1/10 off, calibrate the controller. One major controller manufacturer recommends writing down the readings from the controller in a log book for chemistry along with manual tests (including ORP and temperature). Most facilities only write down PPM and pH from manual tests. Be sure to read and follow the manufacturer's recommendations when it comes to probe maintenance. Clean probes at least semi-annually. Always calibrate your sensors when the factory directions tell you to do so. Other tips include checking chemical feed lines and injection points every few months to ensure chemicals are actually getting into the water. This prevents back pressure and chemical leaks. Finally, some controllers have a "chemical save" mode that allows operators to change the setpoint for periods of time when there are less people in the water.

Water Circulation & Filtration

Pool water filtration and circulation are essential parts of keeping a pool clean and using your chemicals in the most efficient way possible.

Removing debris from pools is an important way to get the most out of your chlorine. Natural debris like leaves, dirt, grass, etc., will quickly eat up your chlorine, and should be regularly removed. Larger debris should be scooped out manually while smaller debris can be left for the filter. Make sure your pool has a turnover rate of no more than six hours to ensure this filtering occurs. Proper water circulation will move the debris to the filter for a cleaner and healthier pool. If the pool pump isn't circulating properly, the water could become stagnant, dirty and filled with debris. Poor circulation can also lead to algae, which, as we've discussed, will create a large chlorine demand. Your pumps and filters are meant to work together. If this team-up does not work efficiently, the chemicals in your water will have to pick up the slack to disinfect and sanitize on overtime.


Keeping your filters clean and ready for debris is a big part of getting the biggest bang for your buck out of the chlorine in your pool. Whenever your sand filters get 8 to 10 psi over their starting level, it's time for a backwash. But, while backwashing is a great way to clean your filters so that they do work efficiently, backwashing too much will dispose of chlorine that you need. Every time you backwash, you're dumping water to waste and will have to replace all of those chemicals, including chlorine, so don't be overzealous with your backwashing.

CYA & pH

Everyone in the pool industry knows about water balance. However, we normally think of it as a way to keep a pool's water clear and safe. We don't typically think of it in terms of increasing your chlorine's effectiveness and stopping problems before they develop.

So, what can you do to conserve what's already in your pool?

First, use stabilizer, also called conditioner or cyanuric acid (CYA), in outdoor pools as it helps protect your free chlorine from sunlight. Pool water without stabilizer can lose up to 90% of its chlorine during one sunny afternoon. Having 10 to 20 ppm stabilizer (CYA) in your pool will help you conserve the chlorine you have, and prevent you from having to add lots to make up for what ultraviolet rays from the sun got rid of. However, too much stabilizer in your pool also decreases your chlorine's effectiveness. Maintaining 10 to 20 ppm of CYA is enough to protect the chlorine in your water. Add too much (>50 ppm CYA), and it lowers the killing power of your chlorine. At a pH of 7.5, chlorinated pool water with no stabilizer in it has a 50/50 mix of hypochlorous acid (HOCl) and hypochlorite ion (OCl-). HOCl is the form of chlorine that quickly and efficiently sanitizes your water. For example, in a pool with 30 ppm stabilizer, that HOCl concentration tanks to around 2%. In an effort to keep your pool clean and algae-free, we recommend to keep your stabilizer levels below 20 ppm.

Secondly, keeping your water within the pH range of 7.2 to 7.6 helps the chlorine you do have in your pool sanitize as effectively as possible without irritating anyone's eyes. Increasing your pH above these levels dramatically decreases the chlorine's ability to disinfect, sanitize and keep your pool clean.

Try Something Different

Since Trichlor is in short supply for your pool chlorinating needs, why not try something different? Calcium hypochlorite, cal hypo, is another common sanitizing product for pools. It comes in tablets and granular form starting at a minimum of 65% available chlorine. Tableted products are NSF-listed for use with flow-through systems that allow you to control the delivery of product according to your bather loads and pool size. Cal hypo contains no stabilizer like Trichlor does, so there is no worry about over-stabilizing your pool. You, the pool operator, decide the level of stabilizer as you will have to manually put it in. Cal hypo has lots of sanitizing power to keep your pool clean and germ and algae-free. You might consider liquid bleach (typically 12% available chlorine), but keep in mind that it can lose its strength rapidly in hot environments, so don't let it sit too long before use. Also, depending upon the size of your facility, you may have to install containment barriers. RM



Samantha (Sam) Williams is a research chemist with Westlake Corp. out of Monroeville Pa. She has been working with and researching water treatment products for nearly the last 10 years. For more information, visit


Samantha Williams

Samantha Williams is a research chemist with Westlake Corp. out of Monroeville Pa. She has been working with and researching water treatment products for nearly the last 10 years. For more information, visit