Free chlorine and total chlorine

Chlorine | Meaning

What is free chlorine?

You know chlorine, of course, from swimming pools and spas. This type of chlorine comes in liquid or solid form. For example, you can think of tablets and chlorine granules. When you throw these products into the water, this form of chlorine is called free chlorine. They call this free chlorine because the "chlorine particles" have not yet bound to the disinfectants in the water at that time. Free chlorine is therefore also called active chlorine.

What is bound chlorine?

When the chlorine particles have bound to disinfectants in the water such as bacteria and algae, this is called bound chlorine. At this stage, the chlorine particle has lost its disinfectant value and must be removed from the water.

What is total chlorine?

Total chlorine is the concentration of free chlorine including the concentration of bound chlorine. 

Chlorine | Chemical Formula

The chemical formula for chlorine is: Cl.

Chlorine | Measurement

It is important to carry out regular chlorine measurements. As described for the concentration of free and bound chlorine, it is important that the proportion of bound chlorine in the total chlorine concentration (total chlorine) never exceeds the proportion of free chlorine. For an optimal disinfecting effect of free chlorine, it is also important that the pH value of the water is between 7.2 and 7.4. This is very close, because when the pH is below 7.2, only 50% of the free chlorine will do its job. At a value above 7.6, the free chlorine will do little or no work.

So, in short, measuring the pH value in the water is also very important and therefore very close. This is why the most reliable systems not only measure the concentration of chlorine in the water, but is often accompanied by a pH sensor.

The measurement of chlorine in the water is usually done in private baths by measuring the ORP/redox value. This is reasonably accurate and relatively cheap. You can read more about this in this article. In addition, free chlorine is also measured in mg/l (milligrams per litre) or ppm (parts per million). Measuring free chlorine is a lot more reliable than measuring chlorine values using an ORP sensor. This is mainly an indirect measure to measure free chlorine in the water. Do you have a public swimming pool or spa? Then always measure the concentration of free chlorine in the water. You are legally obliged to do so.

Recommended values of free chlorine

This is a rule of thumb; if in doubt, always seek advice.

Indoor pool: 0.5 - 1.5 mg/l
Outdoor pool: 0.5 - 3.0 mg/l
Spa, jacuzzi or whirlpool: 1.0 -3.0 mg/l

Especially in public swimming pools, the regulation of free chlorine is very important

Chlorine | Value Increase / Decrease

It is therefore important that the free chlorine value is always higher than the bound chlorine concentration anyway. If these values are out of balance, this can lead to the following problems:

Bound chlorine values are too high.

When the concentration of bound chlorine is too high and the pH value of the water is too low, the chlorine in the water takes on an odour that can irritate the eye, nose and mucous membranes.

The concentration of free chlorine is too low.

When the concentration of free chlorine is too low, there are not enough chlorine particles in the water to remove disinfectants such as bacteria and algae from the water. As a result, the number of bacteria and algae in the water increases. You can see this as the water turns green and cloudy.

The concentration of free chlorine is too high.

So too low a concentration of free chlorine is not desirable, but too high a concentration is definitely not desirable either. High concentrations of free chlorine can cause skin, eye or breathing problems. In addition, a high concentration of free chlorine also causes the water to become cloudy.

Chlorine | Applications

Of course, we all know chlorine from swimming pools and cleaning products. This is partly due to its disinfectant effect. Namely, it keeps bacteria and viruses at bay. However, besides its disinfecting effect, chlorine and its compounds have many other applications:

  • Chlorine is used in some essential medicines because of its harmfulness to bacteria;
  • Purification of tap and drinking water;
  • Purification of pool water and spa water;
  • Bleaching paper;
  • Various chlorine compounds are used for use in consumer products, for example paint, plastics and textiles;
  • Sodium chloride, or NaCl, is a compound used as a flavouring;
  • Polyvinyl chloride or PVC has a huge number of applications.

Disinfection of tap water is one of the uses of chlorine

Chlorine | dosing pumps and systems

Within Emec's product range, we offer various solutions for chlorine dosing. We also offer a number of turnkey packages with dosing pumps incl. sensors.

Dosing pumps suitable for dosing chlorine

For dosing chlorine, we offer two dosing pumps, namely an electromagnetic pump and a motor-driven pump. Both have their own unique features. For instance, the motor-driven dosing pump offers much higher flows and is a priori suitable for industrial applications. In turn, the electromagnetic chlorine pump offers more precision in terms of dosing.

Sensors for chlorine dosing

As described earlier, the degree of chlorine in the water is measured by the ORP / Redox value. In addition, the disinfecting effect of chlorine also depends on the pH value. For both of these characteristics, we offer a number of electrodes. Connected to a controller (Emec Centurio or LDS) or directly to the dosing pump, the system can then automatically regulate the chlorine and pH value in the water.

Prefer a complete chlorine dosing system?

At Emec Webshop, we also offer a number of packages with dosing pump and matching sensor. Both for controlling the ORP value and the pH value. With the Emec Lotus Easy you have at your disposal a complete system for water treatment.a chlorine generator, sensor and dosing pump. We also offer a ready-made panel for controlling free chlorine. Like the Lotus, this system also has an electrode, dosing pump and controller that regulates the dosing of free chlorine. In short, a reliable system for public swimming pools, for example.

About Emec Metering Pumps

Emec is an Italian company that has specialised in dosing systems and measuring equipment for chemicals for over 35 years. This extensive experience and passion for the product is reflected not only in the reliability and innovation of the dosing systems, but also in customer focus. For example, Emec offers a 5-year warranty* (!) as well as excellent after-sale support.

* Warranty applies to the equipment and diaphragm only. Not for the wet parts such as the pump head.

Why Dosing Pump Shop


Request a quote

Name *
Email *
Phone number
Description *