Free vs. Total vs. Combined Chlorine

Testing your pool’s chlorine levels is just as simple as looking at one number, right? Unfortunately, no. There are three different chlorine ‘levels’ that you should track if you’re trying to keep your water balanced.

Free chlorine is the most commonly tracked chlorine level. If you are using test strips, the chlorine reading you’re seeing is likely for ‘free’ chlorine. This level is the amount of chlorine in your pool that is available to help sanitize the water. You should aim to keep the free chlorine level between 2 and 4ppm (parts per million). This amount will provide enough chlorine to sanitize the pool effectively without requiring excessive amounts of chlorine in the water.

Combined chlorine is the amount of chlorine that is already ‘attached’ to something in the water. When you open your pool, and it is very green, the first shock will usually yield high combined chlorine levels. Combined chlorine cannot contribute to sanitizing your water. Using a chlorine shock or oxidizing shock will lower combined chlorine levels, which should be kept to a minimum (below 0.2ppm).

Total chlorine is simply the sum of your free and combined chlorine. This level should be kept below 4ppm. If you manage your free and combined levels properly, you will never have an issue with your total chlorine level. Most commonly, total chlorine will be high after a heavy shock treatment and/or when combined chlorine is not being balanced effectively.