Technical Articles
Technical Bulletin: Monopersulfate - Quick Shock
Monopersulfate is a non-chlorine shock treatment often used in mineral purification systems. Many pool and spa owners like it because it requires only a short waiting period before swimmers can reenter the water. It also cuts down on the odor and irritation caused by elevated levels of chlorine. Monopersulfate is being used more frequently today than it has ever been, primarily due to the rising popularity of the mineral purification systems.
Using Monopersulfate with Chlorine
Chlorine is by far and away the most popular sanitizer used by pool and spa owners. Chlorine quickly and effectively sanitizes pathogenic (disease-causing) bacteria and viruses. Surprisingly, only 10% of the chlorine you add to your pool or spa goes on to kill living organisms. The other 90% of the chlorine oxidizes (destroys) waste products in your water, such as sweat, skin particles, and sun screen introduced into the water by bathers. Chlorine also has to oxidize dust, bugs or grass, which always seem to find their way into the water all by themselves.
The byproducts of chlorine oxidation are chloramines, also know as combined chlorine. These chloramines have a very strong chlorine odor, and they cause nasal and eye irritation. We use shock treatments to get rid of excessive chloramines. Shocking the water with chlorine requires raising the pool or spa chlorine level to approximately 10 ppm. After superchlorinating the water this way, you have to wait until the chlorine residual comes down to the acceptable range, between 1 and 5 ppm, before getting back in the water. This can take hours, depending on how high the chlorine level gets. It is difficult to add just the right amount and the higher the level gets, the longer you will have to wait to get in.
Monopersulfate can eliminate wastes in a pool or spa without the unpleasant side effects of chlorine. While monopersulfate cannot effectively sanitize (kill bacteria) in a pool or spa, you can use it to shock the water. This allows bathers to return to the water sooner-typically less than 30 minutes after you add the monopersulfate shock to the water. Monopersulfate can eliminate impurities through oxidation, and conserve the chlorine residual for killing bacteria. Best of all, monopersulfate does not leave behind any irritating or unpleasant byproducts when it oxidizes wastes.
Monopersulfate with Mineral Purification Systems
Because of the unpleasant odor and irritation associated with chlorine, mineral purification systems and other alternate methods of sanitization have been growing in popularity. These systems use dissolved minerals like copper (to kill algae) and silver (to kill bacteria). While these minerals can keep your pool or spa safe from pathogenic organisms, minerals are incapable of oxidation. So a monopersulfate residual is maintained in the mineral purification systems to oxidize wastes and debris. (In the presence of high levels of chlorine or bromine, monopersulfate dissipates very quickly. In mineral purification systems, where the level of chlorine or bromine is quite low, the monopersulfate residual level will stay in place much longer.) The combination of minerals to sanitize and monopersulfate to oxidize provides protection similar to that of chlorine.
Testing Monopersulfate
Monopersulfate needs to be measured after each use. This ensures proper oxidation of wastes, yielding clear water for bather enjoyment.
There are few kits available to test for monopersulfate. Almost all testing methods have chlorine interference, meaning that the chlorine level interferes with the monopersulfate test results. These tests actually depend on oxidation of an indicator by monopersulfate. Since chlorine is also a strong oxidizer, it usually causes false positive results in monopersulfate tests.
Hach has a subtractive testing method that gives an accurate monopersulfate value even in the presence of chlorine. First, it registers the total oxidizer value by a chemistry that detects both chlorine and monopersulfate. Second, the user completes a test that detects chlorine but not monopersulfate. The difference between the first value and the second value is the monopersulfate value. Accurate measurement of monopersulfate in pools and spas that employ mineral purification systems is easier. Because chlorine is not present in significant concentrations in these systems, test strips or kits that have chlorine interference give correct values despite the interference.
© 2001 Environmental Test Systems, Inc.
Joe Sweazy, Environmental Test Systems, Inc.
