Free Available Residual Chlorine (FRC) is Free Available Chlorine after treating the water with chlorine. That portion of the total available residual chlorine composed of Dissolved Chlorine gas cl2), Hypochlorous Acid (HOCl), and/or Hypochlorite Ion (OCl-) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

In residential pools, there is no legal requirement to use chlorine at all. In fact, many ion users don't. They use a non chlorine shock or ozone and are very happy. However, we are not suggesting or recommending the ion system is an alternative to chlorine alone. There are reports that show that a low level of chlorine and the use of an ion system is a much better way to sanitize than either method alone.

Hypochlorous Acid, Hypochlorite Ions or as dissolved elemental Chlorine. Free Available chlorine is 'free' in the sense that it has not reacted with anything and 'available' in the sense that it can and will react if needed.

Total Residual Chlorine (TRC) is the total of free available residual chlorine and combined (bound) residual chlorine. The amount of measurable chlorine remaining after treating water with chlorine i.e. amount of chlorine left in water after the chlorine demand has been satisfied

Combined Residual Chlorine. Chlorine reacts with organics forming chloro-organics and chloramines. This is a chlorine residual that, because it has reacted with other chemicals in the water, lost some of its disinfecting strength.

Because ozone is a gas and very reactive, it is impractical to establish an ozone residual. Therefore, a chlorine residual is required to protect swimmers.

No. The small amounts of chlorine in your water prevent harmful bacteria growing in the water mains or your pipes. You can rest assured that the usual amount of chlorine in water leaving treatment works is safe and well within the World Health Organisation guidelines.

Chlorine total is the total amount added to the water for treatment. Chlorine free is the amount of chlorine available in the water for treatment. Chlorine total should always be equal to or greater than chlorine free.

Total chlorine is just as it sounds, the total amount of chlorine in the water. However when chlorine binds up with contaminants it forms a compound called "chloramines" that are no longer effective sanitizers and need to be removed through shocking. The chlorine that is still "good" to keep working is the free chlorine. If directions call for maintaining a 1ppm chlorine level, always make sure that matches your free chlorine reading.

YES. The Sigma III is designed to prevent algae and bacteria from growing in your pool water. Occasionally your pool may be filled with an overload of bacteria in a short period of time ( a storm or a pool party, for example). In such instances you will need to oxidize your pool in order to take care of the extreme levels of bacteria quickly. In this situation we recommend using a non-chlorine oxidizer, like potassium monopersulfate.

Developed by OLIN in 1928, this manufacturing process has provided for producing concentrated chlorine. This process was called “High Test Hypochlorite.” Nowadays, it is better known as its abbreviation, HTH. Calcium hypochlorite is often called “granular chlorine”. It is the form of chlorine most used by pool owners. First produced in 1785 by hypochlorite was produced in a chemical plant in Javel, France. Sodium hypochlorite is only stable as a solution.

Pool and spa water treatment with chlorine and other halogen disinfectants (bromine) require maintaining a residual concentration of at least 1 to 3 PPM (Part Per Million) in water. The effectiveness of the use of these chemicals is controlled by many variables: pH, dissolved solids, temperature and halogen concentrations. Under EPA urging, most municipalities now restrict the from dispensing and storage of chlorine.

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Neither chemical fumigation nor ThermaPureHeat® have a residual effect. They kill what is in the house, but won't kill anything entering after the treatment.

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