Chlorine is both a sanitizer and an oxidizer. Its low cost relative to other sanitizing chemicals makes it a popular choice for swimming pools; however, it isn’t very stable at high temperatures, which is why in spas it’s more often used as a shock than a routine sanitizer.
Chlorine also dissipates quickly in sunlight. On a sunny day, as much as 95 percent of active chlorine can be lost in just two hours. That’s why chlorine is often paired with a stabilizing agent such as cyanuric acid. There are several types of chlorine, and some such as dichlor and trichlor are more stable than others.
It’s important to note that some types of chlorine affect pH more than others, so you’ll want to take that into account when balancing your spa water and choosing a chlorine sanitizer. A high pH drastically reduces the effectiveness of chlorine because it accelerates the rate at which chlorine molecules break down. Spas that operate at high pH levels require higher levels of chlorine to kill algae and bacteria.
After chlorine is no longer able to kill organisms, it combines with contaminants in the spa to form chloramines, nasty little molecules that can irritate eyes and skin and cause a strong chlorinelike odor. Although many people assume that a strong chlorine odor is an indication that there is too much chlorine in the water, actually the opposite is
true. The strong odor usually means that the chlorine in the water is no longer an effective sanitizer and chloramines have formed. The solution to this problem is to superchlorinate or âœshockâ the water with an oxidizer to eliminate the chloramines.
Testing Chlorine Levels. Easy-to-use test strips and complete test kits are available from spa supply dealers. You’ll want to measure âœfree availableâ chlorine the portion of chlorine that’s capable of sanitizing, killing germs, and oxidizing organics. When free available chlorine reacts with ammonia waste, it becomes âœcombined chlorine,â also known as chloramines. Whereas free chlorine has no detectable taste or smell at levels up to 10 to 20 ppm, combined chlorine levels as low as 0.2 ppm can create the familiar odor common to heavily used spas (and pools). Combined chlorine has few sanitizing capabilities. For spas, the recommended level for free available chlorine is 3 to 5 ppm.
Adjusting Chlorine Levels. Chlorine comes in many forms: liquid, granular, tablet, stick, and gas. Granules are the most common form used in spas. They are easy to measure and apply, and accidents are less likely to occur because the dry chemical won’t splash. To apply granules, carefully sprinkle them as close to the center of the spa as possible, where they have the best chance to circulate and dissolve before coming in contact with the spa’s surface. To distribute tablet or stick chlorine, place the tablets or sticks in a floating or in-line dispenser. As water flows through the dispenser, the chlorine is slowly dissolved and released. Some chlorine products contain more free available chlorine than others, so follow the manufacturer’s guidelines to determine the correct dose for your size spa.