Aquachek Total Chlorine Free Chlorine Test Strips

Chlorine is used as a sanitizer / disinfectant in many applications. Often, levels above 1ppm in water can be detected by smell or taste

Total Chlorine

Chlorine in pool and spa water may be present in two forms. It is free chlorine that does the hard work of killing bacteria and oxidizing contaminants. (When you add a chlorine compound like Cal-Hypo or trichlor to your pool, you are actually adding free chlorine.) When the free chlorine combines with these contaminants, such as oils, swimmer waste and other organic compounds, it becomes combined chlorine, or chloramines. In pool and spa water, this form of chlorine has very little sanitizing ability, and no oxidizing ability. You can think of combined chlorine as a spent bullet.

Total chlorine is just the sum of both combined chlorine and free chlorine. In other words,

(total chlorine) = (free chlorine) plus (combined chlorine)

Knowing your total chlorine and free chlorine levels allow you to calculate combined chlorine (combined chlorine = total chlorine minus free chlorine). If the total chlorine level is higher than free chlorine, it is obvious that combined chlorine is present. In that case you need to shock or superchlorinate your pool or spa. To shock the pool, you add a free chlorine compound in an extra large dose. The high dosage of free chlorine will actually oxidize (destroy, burn off) the combined chlorine.

 Free Chlorine

Every sanitizer has two key functions, to sanitize (kill bacteria and all living organisms) and also oxidize (destroy contaminants and waste). The most popular pool and spa sanitizer is chlorine. Chlorine is also classified as a disinfectant, meaning that it is capable of killing bacteria, algae and other organic material instantly. All chlorine does the same thing when it is added to the water, regardless of the type of chlorine added. It forms free available chlorine. Free chlorine is the form of chlorine that kills bacteria, algae and disease-causing organisms. It is the attack dog that guards your pool against microbiotic intruders. (In general, you wouldn’t want a dog in the pool, but this is an exception.)

You must maintain free chlorine at a sufficient level to disinfect potential contaminants on contact. The more chlorine in the water, the more it can sanitize and oxidize the water. (Remember that sanitizing and oxidizing are the processes that chlorine uses to keep the water clear and clean.) However, if the free chlorine level gets too high, it can make the water uncomfortable for swimmers. The trick is to keep the free chlorine level in the ideal range. In a swimming pool, keep free chlorine at a minimum of 1 ppm (parts per million) and a maximum of 10 ppm, with an ideal concentration of 1 to 3 ppm.

In spas the level needs to be maintained at a slightly higher level due to the smaller volume and higher temperature. The minimum level should be 2 ppm in a spa, again no higher than 10 ppm, and ideally 3 to 5 ppm.