What Is Free Chlorine and Why is It Important in Your Pool?

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If you didn’t know, chlorine is undeniably the most important chemical in your maintenance tool belt. While it may cause the water to sting your eyes, the chlorine will effectively keep your pool balanced and clean. Furthermore, this chemical will work hard to kill any nasty bacteria or microorganisms that can grow in your pool and impact your relaxation time.

What is a FAS-DPD Test?

A FAS-DPD test stands for ferrous ammonium sulfate and N, N-diethyl-p-phenylenediamine, which refers to the chemicals used to measure your FCL and CC levels. Next, add the DPD to your pool water sample, which will react with the chlorine to produce a pink color. Next, you will want to add in the FAS drops until the pink color disappears. So the number of drops needed to turn the water colorless determines your CC levels.

What are the Different Types of Chlorine for Pools?

Most pool owners use three different types of chlorines when treating their pools. Free chlorine (FCL), combined chlorine (CC), and total chlorine (TC) are the three types of chlorine that pool owners need to remember when attempting to balance a pool. You can measure the different levels of chlorine with some help from a FAS-DPD test.

Combined Chlorine

Pool Calculator describes combined chlorine (CC) as an intermediate breakdown product used in pool sanitization. This type of chlorine gives off that signature chlorine smell in your pool. If your CC rises above 0.5, then your FCL isn’t appropriate. Thus, you’ll have to shock your pool.

Total Chlorine

Total chlorine (TC) refers to the sum of free chlorine and combined chlorine present in your pool. You can check your total chlorine by using the results from the FAS-DPD test. Moreover, TC will become useless if your combined chlorine levels become too high. If this occurs, then you can expect a visit from algae and other harmful microorganisms.

Free Chlorine

Lastly, free chlorine (FCL) refers to the amount of chlorine in your pool, which hasn’t yet mixed into the chlorinated water to sanitize any harmful bacteria or microorganisms that can grow in a pool. This type of chlorine is the most important because the chlorine keeps actively sanitizing your pool. Keeping your FCL between 1.0-3.0 ppm will ensure a healthy balance of chlorine to prevent any harmful organisms from growing.

If your FCL gets too low, using calcium hypochlorite will bring the levels back up. The American Chemistry Council describes calcium hypochlorite as a white solid powder that eliminates harmful germs when placed in a pool. These germs can cause potential health problems for pool swimmers, such as painful infections in the ear, nose, or throat.

How to Shock Your Pool When FCL Levels Get too Low 

You’ll need to shock your pool when one of three things occurs: algae growth, your pool’s FCL reaches zero, and the CC rises above 0.5 ppm. Try shocking your pool at night because the sun will burn off the shock, leaving the chemical to work improperly. Shocking the pool at night also gives the chemicals enough time to work, allowing you to use your luxury pool the next day.

  1. The first step to shocking your pool is to test the pH level in your pool by using a test kit or your FAS-DPD test. Understanding your pool’s chlorine levels will better allow you to estimate how much shock to put in your pool.
  2. You will then need to calculate the amount of shock to put in your pool, which you can find on the product’s package. Also, don’t forget to protect your skin by wearing gloves.
  3. Using granular pool shock may prove easier to handle than liquid pool shock because it is a pre-packaged amount that has to dissolve in a bucket of water before use. But using granular will help prevent calculation mistakes.
  4. After you have the correct amount of shock mixed, make sure that your pool pump is running before pouring the mixture around the edges of the pool. The pump should run for about six hours and then later test the water to ensure the chlorine levels are back to their recommended 1.0 to 3.0 ppm levels. It is important to wait for the chlorine levels to return to normal before you go in the pool because high chlorine levels can cause skin and eye irritation, and damage your clothes.

Considerations for Saltwater Pools

If you have a saltwater pool, add your salt to the pool and the salt chlorinated generator will take care of the rest. You can also shock your saltwater pool the same way you’d typically shock a chlorinated pool; just remember to check your chlorine levels before and after to avoid further mishaps.

Check Your FCL and Other Chlorine Levels Regularly!

It is always important to have appropriate chlorine levels in your pool, so be sure to check them two to three times when your pool gets a lot of use during the week. Letting your chlorine levels get too low could allow harmful bacteria and microorganisms, potentially harming any unsuspecting swimmer.

Shoreline Pools offers a staff 24-hours a day, 7-days a week, and can help determine the best way and how to shock your pool if you have never done it before. Our employees hold advanced certifications and use the best products to ensure your pool receives the treatment it deserves.

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