Do Pools Need More Chlorine When It’s Hot?

As you order supplies to prepare your pool, you need to make sure to have plenty of chlorine on hand for sanitization and oxidation purposes. However, when the months grow hotter, will you need to increase your supply of chlorine?

Typically, pools burn through more chlorine during hotter months. The combination of increased swimmers, intense sunlight, and higher temperatures increases the amount of chlorine needed to sanitize the pool and how quickly the water evaporates. 

Of course, just like in other times of the year, you will want to ensure frequent testing of the chlorine levels during the hotter months to make sure that the chemical levels are correct for your pool based on its size, use, and more. Let’s take a closer look as to why your pool may run through more chlorine when it’s hot, appropriate levels to ensure safe and sanitary swims, and simple tests for maintaining appropriate chlorine levels in your pool. 

Does My Pool Need More Chlorine When It’s Hot?

As the weather starts to warm up, you will likely begin preparing your pool for the fun that is sure to ensue in the warmer months. There are many different components that go into keeping your pool clean and safe for swimmers to use. One of these, of course, is using chlorine to keep the water sanitized and oxidized. Chlorine-based pool sanitizers are great for reducing swimmers’ risk of waterborne illnesses, ensuring safety and sanitization for swimmers in your backyard pool.

It is important to maintain the right chlorine levels in your pool at an optimal level. For your residential pool, you need between 2 to 4 ppm; commercial pools will need 3 to 5 ppm of chlorine to be safe. The amount will depend on the size of the pool but will likely increase when it’s hot. 

Pool owners will need to test the level of chlorine that is found in the pool regularly. This will ensure that you have just the right amount of the sanitizer/oxidizer inside the pool at all times. In warmer temperatures, however, you may begin to notice that the chlorine you have added is used at higher rates. If you are noticing this in your pool tests, you will need to add more chlorine to the pool to sustain the appropriate chemical levels.

While it is not always true, a good rule of thumb to keep in mind is that once the temperature reaches 80℉, you will need to add about 50% more chlorine to the pool for each 10-degree increase in temperature. Of course, this will need to be measured on the spot, but these estimates can help you to plan ahead for the typical use that you can expect, depending on your climate.

Why Does My Pool Need More Chlorine When It’s Hot?

So, we have mentioned that, yes, pools typically require more regular additions of chlorine as the temperatures become hotter. Still, you are likely wondering why exactly this is.

Pools need more chlorine due to the level of sanitization required with more swimmers. The more use your pool receives (in hot months), the more organic material will need to be disposed of by chlorine. Second, chlorine reacts with the sun and heat and will be more quickly evaporated in the heat.

Many people have traditional days where they open and close their family’s pool in their backyard. These days typically fall around the day that the weather will finally be warm enough, and the day that the weather will begin being too cold, respectively. 

As more people begin using your pool on hotter days, more chlorine will be needed to sanitize and oxidize the water (yes, it does both of these things). Free chlorine will react with organic material and get used up when more people spend their time in the pool. 

In terms of the increase in heat (increased sun exposure and higher temperature ranges) in combination with chlorine, free chlorine can also interact with the sun and heat.  Chlorine will slowly start to form some hypochlorite ions in the water. These break apart when UV radiation hits them, releasing some chlorine gas into the air. 

On those really sunny and hot days, it is possible that the light will reduce the amount of chlorination in the pool by 90% in just one day. This is why frequent testing is important. 

Chlorine is also affected by temperature. Many organisms and bacteria will grow better when the environment warms up. When the temperature increases, it will use up the chlorine more quickly, and you will need to add more to the pool to keep it safe. 

How Much Chlorine is Enough?

As you work on your pool, it is important to consider how much chlorine you will need to help keep the pool clean and safe. The exact amount that you need will depend on the size of the pool you have as well as the pool usage. 

The recommended amount of chlorine for a pool is between 2 to 4 ppm for a traditional residential pool. This level will help kill off harmful bacteria and viruses while keeping the water safe to swim in. Be sure to test the appropriate chemical levels based on your unique pool size, usage, and environmental factors.

If you do not put enough chlorine into the pool, then it is going to be ineffective. This means that there simply will not be enough chlorine in the pool to ensure sanitization or oxidation is occurring. Both of these processes are incredibly important to eliminating bacteria and supplying fresh oxygen to the water (and preventing bacteria buildup).

Most testing options will recommend that you keep the levels closer to 3 ppm to make sure all the bacteria are killed without causing the negative effects of adding too much chlorine. Of course, be sure to test for what is recommended for your unique pool specifications. 

Can I Add Too Much Chlorine?

As you are adding chlorine to your pool, you may think that it is better to add as much as possible to save time and to kill everything off. But is it possible to add too much chlorine to your pool?

It is possible to add too much chlorine to your pool. Anything over 4 ppm is too much for a residential pool and can cause harmful side effects to swimmers. Excess chlorine does not provide any additional protection against pathogens or bacteria and can lead to harm to swimmers and the pool itself. 

There are several harmful effects of too much chlorine in your pool. For those who jump into the pool, you may notice they experience rashes, coughs, pain in their throat and nose, eye irritation, and problems with asthma. Chlorine is toxic if you have high levels of it in the pool, which is why testing it is so important. Especially since chlorine both sanitizes and oxidizes the pool, it is incredibly important to ensure appropriate levels (along with appropriate levels of all other chemicals used in your pool).

If you are running tests on your pool chemicals and notice that the levels of chlorine are too high, you may need to wait a few days to begin using the pool until the levels begin to balance out. Or, you can add in chemical solutions to counteract this balance, but waiting it out is a more standard procedure.

How Can I Test the Chlorine Levels In My Pool?

It is almost impossible to know how much chlorine is in your pool at any given time without testing it first. There are different methods you can use to see the exact amount of chlorine that is in your pool at any given time. 

To test the chlorine levels in your pool, you can use several methods including chlorine test strips, chlorine test kits (drops), an electronic chlorine tester, or an automatic chlorinator and tester. These will give you accurate results on how much chlorine is in your pool at the time. 

Testing your pool does not need to be difficult. The easiest method is to use chlorine test strips that you keep on hand. Most of these are made out of plastic with some chemical pads on the side meant to find the chlorine. You can use these with the following steps:

  1. Open up the pool. Wash your hands before using the test strips.
  2. Take a test strip from the container and dip it into the pool.
  3. Leave the test strip in the water for a few seconds and then remove it. 
  4. Compare the color to the one on the package to see how much chlorine there is. 

The other methods are very similar. The chlorine test kits will use a similar process but will use a re-agent to help measure the chlorine content. The electronic tester can be dipped into the pool and will give an accurate reading too. Automatic chlorinators and testers can help you monitor the chlorine constantly so you know exactly when it runs out. You can choose which option you like the best to keep the pool clean and oxidized. 

Keeping Your Pool Safe in the Heat

There are different cleaning agents you can use to help keep your pool safe during the summer, but chlorine is one of the most effective and easy to use. When you add the right amount to your pool, and test it frequently to make sure it stays at the right levels, you will keep everyone safe in your pool- even on those incredibly hot days. 

Jed Arnold

Jed spent every year from the ages of 15 - 22 as a Lifeguard (Red Cross) and ages of 17 - 22 as a Certified Pool Operator (CPO). Between working for over a dozen facilities and owning a pool, he carries over a decade of pool experience.

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