What is the Difference Between Combined, Total, and Free Chlorine?


Chlorine is a necessary chemical for keeping swimming pools clean and free from harmful bacteria.

There are three main types of the chlorine-combined, total, and free.

  1. Free chlorine
  2. Combined chlorine
  3. Total chlorine

Knowing how to test for and maintain these levels is critical in keeping your swimming pool clean, clear, and safe to swim in.

1. The different types of chlorine and what each one means

Free chlorine is the measurement of just the free form of chlorine in the water. A free chlorine measurement is the amount of chlorine that hasn’t been combined with chlorinated water to effectively remove contaminants, allowing this chlorine to destroy dangerous microbes in your pool’s water.

Combined chlorine is made when free chlorine is combined with other chemicals in the water, and is unable to sanitize or purify the water.

Total chlorine is the measurement of all forms of chlorine in the water-free and combined. The total chlorine content is the sum of combined chlorine and free chlorine (combined chlorine + free chlorine = total chlorine).

The amount of free chlorine in your pool is the most important factor when it comes to sanitizing. This implies that this chlorine is freely available to eliminate dangerous germs from water in your swimming pool since it has yet to combine with chlorinated water to successfully sanitize pollutants.

Knowing how to test for and maintain these levels is critical in keeping your swimming pool clean, clear, and safe to swim in.

2. How to test for free chlorine levels

test free chlorine

Test Strips

They’re simply used to determine total and free chlorine levels. Test strips are a semi-quantitative, visual technique for detecting both free and total chlorine. The indicator is applied to the strip, which changes color if the required parameter is present.

The main disadvantage of determining chlorine concentration using test strips is that the result is in a range rather than a specific number and the colors can be interpreted differently from person to person.


The DPD test is the most common technique for determining chlorine levels in water samples. The DPD approach is a colorimetric procedure for measuring free and total chlorine concentration.

In the presence of oxidizing agents such as chlorine, DPD is a colourless chemical that changes color to magenta pink. To determine the amount of combined chlorine present, potassium iodide may be added in a second step to the reaction.

DPD is the only colorimetric technique that distinguishes among various types of combined chlorine.

DPD is a sensitive detection method that can measure up to 10 mg/L free chlorine in a sample volume of only 0.5 mL. However, because reagents are prepared with higher amounts DPD in smaller sample volumes, measuring up to around 10 mg/L free chlorine is possible. Measuring a wider range of free chlorine using DPD would necessitate dilution of the sample, which will extend testing time, increase complexity, and affect accuracy.

Potassium Iodide Colorimetric Method

The use of potassium iodide reagents for detecting higher chlorine levels in water samples is common. When chlorine reacts with potassium iodide in an acidic solution, iodine is released, turning the liquid brown. The color of the solution may be used to determine chlorine concentration using visual or photometric techniques.

This technique can be used to estimate chlorine levels as high as 0.5 mg/L of free chlorine and above, although it is not sensitive to free chlorine and only provides a reading for the amount of total chlorine in the sample.

What is the right amount?

To adjust your swimming pool water, you must do what is called chlorination breakpoint. This will raise the chlorine level in your pool to a point where it is very efficient at destroying germs and disinfecting the water. This is critical for keeping swimmers safe and keeping the water in the pool clear.

Let’s assume you have a pool that is 25,000 gallons in capacity. The chlorine level should be maintained at between 1.5 and 3 milligrams of free chlorine per liter when there is enough dissolved oxygen (DO). Between 0.2 and 0.4 mg/l total chlorine are needed for complete sanitation; the lower amount suffices for maintenance because although it isn’t exactly clean, it does keep the water from suffering from too many impurities on account of its large surface area (also known as surface tension).

The Calculation. You know that free chlorine plus combined chlorine equals total chlorine. You subtract the amount of free chlorine from the total chlorine to get your combined chlorine level.

You must add chlorine to your pool to match the amount of demand determined by your own pool. In order to get the correct chlorine concentration in your pool, you will need to multiply this measurement by 10.

A good rule of thumb is to create free chlorine in a pool by using the higher ten times multiplier to ensure you have adequate chlorine concentration. Having a little extra chlorine in the swimming pool as a precaution is a good thing.

How can I increase the amount of free chlorine in my pool water?

chlorine tablets to increase free chlorine

The amount of free chlorine in a swimming pool’s water is increased when chlorine is added. So, keep this in mind: your chlorine level should be between 1 and 4 ppm. The ideal concentration is usually 3 ppm.

There are a plethora of ways to raise the chlorine level in your pool. Liquid chlorine and powdered chlorine are two examples. Granulated (non-stabilized) chlorine, on the other hand, is advised by experts. It’s a much more powerful chemical. Here are some of the most effective strategies for manually increasing your pool’s chlorine level.

Raising the chlorine level with dichlor granules

Pool surfaces, for example, are often textured with dolomite or other calcium-based chemicals to increase resistance against algae. Dichlor granules are primarily used in pools, hot tubs, and jacuzzis. Sodium dichloroisocyanurate is a similar product that is usually intended for above-ground pools. There are benefits and drawbacks to all of these materials, as we’ve seen before.

The fast-dissolving qualities of dichlor are one of its top advantages. This feature allows you to rapidly increase the amount of chlorine in your pool. Furthermore, dichlor will not affect the overall alkalinity in your pool. Finally, the pH level will be unaffected by dichlor. This is ideal for spas because it has a very little impact on the pH level

When trying to quickly raise the chlorine level in your pool, consider using chlorine-based shock. There are two choices: chlorine-based shock and non-chlorine-based shock. Non-chlorine-based shock will increase the total amount of chlorine, whereas chlorine-based will decrease combined chlorine. This can be beneficial if the total amount of chlorination is too high.

The most important component of chlorine-based shock is calcium hypochlorite. Calcium hypochlorite, also known as inorganic chloride, is a bleach and chlorine product that’s used worldwide. If you want to raise the chlorine concentration by at least 10 ppm, you should only use chlorine-based shock.

3. How to maintain chlorine levels

Depending on the environmental conditions like if it rains frequently, you may need to add chlorine more often than usual to keep up with the demand. Be sure to test your chlorine levels regularly so that you can make any necessary adjustments.


  • It’s not a good idea to mix chlorine from different manufacturers. Not only will mixing different brands of chlorine make keeping track of your pool’s chlorine level more difficult, but it can also be harmful to your health.
  • It is not advised to use liquid bleach. Determining how much chlorine was actually added to your pool after pouring a couple of bottles is difficult.
  • To avoid problems, don’t use too much chlorine. This might be detrimental to your health. If you’re unsure how much chlorine you’ll need, test the water and add a little at a time until you’ve reached the desired level of chlorination.
  • Pouring chlorine straight into the skimmers is a common blunder. What’s the problem with doing it like that? There are several reasons why pouring chlorine directly onto your skimmers should be avoided. Why? Pouring chlorine straight in to the skimmer will cause your pool’s pH level to drop. As a consequence, over time, your pool’s equipment will corrode away.

If you can’t seem to achieve the appropriate level of chlorine due to a variety of factors, there are two things you may try. Your first choice is to completely empty your pool and then fill it with new water. The alternative option is to utilize unstabilized chlorine. If you choose this route, start by adding a little and testing the water after each addition. Continue until your level is where it should be.


The proper free chlorine level in your swimming pool is critical for keeping it clean and safe. In this article, we’ve explained the difference between combined, total, and free chlorine and how to test and maintain these levels.

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