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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. In this article, we will discuss free chlorines 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 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.

Not having enough chlorine 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.

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? It’s not as easy as you think and you have to be careful while doing it, so you do not throw your pool water completely out of balance in the process.

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.

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. If you are not going to look at one chlorine measurement than ignore total chlorine because free chlorine is much too critical to proper pool water chemistry to overlook.

Josh Hurd

James Radosevich

Saturday 20th of June 2020

I am a little confused. Can you help me? I have a 10,000 Gal above ground pool (30 yrs) How do I lower my Total Chlorine to be equal to my Free Chlorine?

ADDING MORE LIQUID CHLORINE PLUS A SUPER SHOCK RAISED BOTH THE TOTAL CHLORINE AND THE FREE CHLORINE. IT WAS TOTAL CHLORINE - FREE CHLORINE = 3 ppm – 1 ppm = Chlorine Demand = 2 NOW IS I Added 40 ounces Liquid Chlorine + 1 pound super Shock: TC= 15, FC=4, CHLORINE DEMAND = 9 I am hesitant to add 10 times that amount of Chlorine. Should I Super Shock with Ten Bags of SS?

Thank You for the article.


Wednesday 27th of May 2020

I know as much now as I did before I read this article. Guess I will go to the pool store for real help