How to Raise Free Chlorine in Pool? - Some Helpful Suggestions

Keeping water in a swimming pool clear and balanced is not an easy thing to do. That’s because there are so many different things you have to keep an eye on as far as water chemistry is concerned.

Most people realize the importance of chlorine and shock in keeping pool water clear, but there are other important pool chemistry components that are often overlooked. One of those is free chlorine.

Basically, you can increase the level of free chlorine in the water by increasing the chlorine amount. However, you need to make sure you are not messing with the chemical balance of your pool.

In this article, we will discuss free chlorine’s role in pool chemistry and how to raise it once it has gotten too low.

What exactly is free chlorine?

Most people, when they test their pool water chemistry, they make sure they look at the chlorine level in the pool. They often don’t pay any attention to free chlorine at all. As a matter of fact, some test kits do not even test for free chlorine. This is not good for several reasons.

When you test a sample of your pool water and check the total chlorine level, it can be misleading. That’s because that reading includes all of the types of chlorine found in your swimming pool.

The problem is, some of that chlorine that the test kit indicates is in the pool is actually useless (called chloramines or combined chlorine). That’s why you need to test for free chlorine. It’s an actual measurement of the amount of chlorine in your backyard pool that is still available to act as a sanitizer.

Free chlorine is a measurement of what is called hypochlorous acid and the hypochlorite. These are the good parts of chlorine that are active and able to change chemically to sanitize your pool. Why do you want to measure free chlorine as opposed to total chlorine? It’s because free chlorine is 25 times more effective at sanitizing pool water than used up combined chlorine is.

What is the right amount?

To properly adjust your swimming pool water, you will have to do what is known as ‘breakpoint chlorination‘. This will bring your pool water chlorine back up to a level where it’s very effective at killing organisms and disinfecting the pool water. This is very important to help keep swimmers safe and keep the water in the pool clear.

Here is the part where total chlorine comes into play. You know that free chlorine + combined chlorine = total chlorine. You subtract the amount of free chlorine from the total chlorine to get your combined chlorine level. This figure is what is known as ‘chlorine demand. ‘

Once you know what the amount of chlorine demand is for your backyard pool, you will need to add chlorine to your pool to meet this figure. You will actually have to multiply this figure by 10 in order to get the right chlorine dosage to add to your pool to get its chlorine level right.

In truth, multiplying the chlorine demand figure by 7.6 is enough. Pool professionals who know how to raise free chlorine in pool use the higher ten times multiplier to make sure they have enough chlorine in the pool. You have to properly match total chlorine to free chlorine. They also realize that having a little extra chlorine in the swimming pool is a much better alternative than having too little.

What causes low free chlorine in pool?

There are many occurrences that cause chlorine in a pool to be used up at a higher rate. Things that cause low free chlorine levels are excessive sunlight, high bather loads, and improper water chemistry.
An increased organic activity in your swimming pool will also cause the little bit of chlorine that’s in there to be used up faster too. Even acid rain and other biomatter getting into your pool will cause free chlorine levels to drop.
If you have a chlorine feeder, your pool might not have enough salt. Also, your chlorinator or salt cell could be faulty.
If you have a low cyanuric acid (CYA) reading, this will cause low levels of free chlorine.

How to raise free chlorine in pool water?

OK, so you have tested the water in your swimming pool, and you determine that you have low free chlorine in the pool. The next question is, how do you raise the free chlorine level back up?

When chlorine is being added to a pool, the amount of free chlorine residing in the water is being increased. So, just remember that your chlorine level should be anywhere between 1 and 4 parts per million (ppm). Ideally, the perfect level is 3 ppm.

There are a couple ways you can do this, with liquid chlorine or granulated chlorine. However, experts recommend granulated (non-stabilized) over liquid. It’s a much more powerful substance. Listed below are some of the most useful ways to manually raise your pool’s chlorine level.

Using trichlor to raise the chlorine level

Trichlor, also known as trichloroisocyanuric acid, is a very common product used by pool owners, especially individuals with outdoor pools. Some of the benefits of trichlor include first its slow-dissolving properties. This makes trichlor the perfect choice for individuals with a chlorinator.

Another benefit of trichlor is the many choices you have. These include sticks, pellets, pucks, and granules, and the best part? Trichlor products are quite inexpensive when compared to other chlorine products.

As great as trichlor is, there are some disadvantages as well.

Trichlor is extremely concentrated. As a result, getting even the smallest bit on you can cause your skin to burn. Getting a lot on your skin could mean a trip to the emergency room. When using trichlor, avoid inhaling any of the fumes. Wearing a protective facemask when using this chemical can also be beneficial to your health.
Another drawback to using trichlor includes the damage it can do to your pool. Trichlor has a low alkalinity level and, as a result, can corrode walls and equipment within your pool. To counter this issue, you may have to pour a little soda ash (sodium bicarbonate) into your pool water.

Raising the chlorine level with dichlor granules

Dichlor granules are mainly used for indoor pools, spas, hot tubs, and Jacuzzis. Sodium dichloroisocyanurate is a similar product but typically designed for above-ground pools. Just like the products we already covered, there are advantages and disadvantages.

Some of the advantages to using dichlor include its fast-dissolving properties. Because of this quality, dichlor allows you to quickly increase the chlorine. In addition to this, dichlor will not affect the overall alkalinity in your pool. Lastly, dichlor will have a very minimal effect on the pH level. This is great for spas.

Although there aren’t too many disadvantages, there are a couple.

Dichlor is a more costly product than trichlor. So, you can expect to pay more at the register.
The second disadvantage of Dichlor is that it doesn’t work well with chlorinators. That’s because it’s a fast-dissolving solution.

Shocking your pool to raise the chlorine level

People who are wanting to rapidly increase the chlorine level in their pool should think about trying chlorine-based shock. You really have two options, there’s chlorine-based shock and non-chlorine-based shock. Chlorine-based will quickly increase the level, while non-chlorine-based will reduce combined chlorine. This is useful if your chlorine level is too high.

The main ingredient in chlorine-based shock is calcium hypochlorite. Calcium hypochlorite is an inorganic compound used for a variety of bleaching and chlorine products. You should only use chlorine-based shock when you need to raise the chlorine level by at least 10 ppm or more. Here are a few other tips when it comes to shocking your pool:

Always follow the directions listed on the side of the package. Never take shortcuts.
Always consider your pool size when determining how much chemical to use.
After you shock your pool, make sure you don’t cover it with a tarp or covering. The reason being is because the water needs to come in contact with the air. This will let the oxidation gasses escape freely.
Try and shock your pool on a cloudy day. The bright sunshine will decrease the pool’s chlorine level.

Why do I constantly have a low free chlorine reading?

If you constantly have low free chlorine levels in your pool, it’s best to try and figure out why. Listed below are a few of the reasons you may be having problems.

A low salt level in your pool can cause your chlorine level to constantly be low. For your chlorinator to work properly, there has to be enough salt in your pool. Otherwise, your chlorinator can’t create chlorine. To fix this problem, you’ll need to add salt. It’s recommended that your pool’s salt level should be at 5,000 ppm. Just remember that for a 16,000 gallon pool, a 44 lbs bag of salt comes out to about 500 ppm.
Another reason your chlorine level may always be low is because your salt cell needs a good cleaning. How do you do this? You’ll need to perform a hydrochloric acid bath. You’ll want to do this in 10% acid and 90% water. The recommended duration of this bath should be around 4 minutes. You’ll know you’re finished when you see the calcium bubbling up and slowly dissolving.
If your chlorinator salt cell or chlorinator is old, then it may not work properly. In this case, you’ll need to replace it. Generally speaking, these devices last anywhere between 7 to 10 years. With a lot of these machines, the PCB board or the power board is the problem. It’s always best to check your warranty when you find yourself in this situation.
Lastly, your pool’s cyanuric acid (CYA) level may be low. As a result, the greater portion of the chlorine in your pool’s water just might evaporate very quickly in the sun. If this is your issue, you’ll want to add cyanuric acid to the water. Make sure you follow the guidelines displayed on the package. As a simple rule of thumb, it’s best not to add any more than 20 ounces at once.

What happens when your pool’s free chlorine level has been low for a long time?

If you think your pool’s chlorine level is low, it’s best to handle this situation as soon as possible. Otherwise, low chlorine levels over a long period of time can lead to several problems like:

Microorganisms will start to grow and produce in your pool. This can include bacteria like E. coli, shigella, campylobacter and salmonella. These bacteria can potentially make your family and friends sick if they swim in the pool.
Algae growth is another issue that can arise when your pool’s chlorine level has been too low for too long. Black algae and mustard algae are the worse kinds, because they’re hard to remove once they’re made their presence known.
Cloudy water can also become an issue when your pool’s chlorine level is too low. This makes a pool look trashy and unpleasant to your guests.
Lastly, not keeping your pool’s chlorine level where it should be can cause damage and unnecessary maintenance like corrosion and algae stains.

A few final tips on adding chlorine to your pool

A big mistake pool owners make is pouring the chlorine directly onto their skimmers. This is a bad idea. Why? Pouring chlorine right onto the skimmer will decrease your pool’s pH level. As a result, your pool’s equipment will become corroded over the years.
It’s really a bad idea to mix different brands of chlorine. Not only will this make controlling your pool’s chlorine level harder, but it’s also can be dangerous to your health.
Using liquid bleach is not recommended. Figuring out how much chlorine was actually mixed into your pool after dumping a couple of bottles is quite difficult.
Avoid adding too much chlorine. This can be dangerous to your health. If you’re unsure how much chlorine you need, test the water, add a little, and then the water again. Repeat this process until you get your chlorine level right.
Pool owners who use a floater might want to tie the device to where the water flows the best. This will distribute your chlorine much more evenly.
It’s recommended to keep extra chlorine put away, so you’ll always have it on hand. This way, you can quickly fix a low chlorine issue.
If your pool’s cyanuric acid is at 80 ppm or higher, then you’ll need to fix the problem. There are two things you can do. Your first option is to completely drain your pool and then add new water. Your other option is to add unstabilized chlorine. If you go with option two, you’ll want to add a little and then test your water. Repeat this process until your level is where it should be.

It’s important to keep a close eye on your free chlorine

So be sure to pay close attention to the free chlorine level in your pool every time you take a test reading of the water. You now know how important it is to know the amount of chlorine in your pool that’s free and available to act as a sanitizer.

Keeping your free chlorine at the proper level will help your pool water be safer to swim in and keep it clear and pleasant to look at too. Staying on top of your free chlorine level regularly will also prevent unnecessary problems in the future.

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Josh Hurd

Josh Hurd has been freelance writing since 2006. He attended the University of Akron, graduating with a Master of Fine Arts in creative writing.