Biguanide products (pronounced: buy-GA-WHY-nide) are approved for use as a sanitizer in pools and spas by the U.S. Environmental Protection Agency (EPA). While there are no regulatory issues with using them in residential pools and spas, many jurisdictions do not allow biguanide sanitizers to be used in commercial pools and spas. For reference, one major manufacturer states that its biguanide based sanitizer is best suited for pools under 25,000 gallons.
Liquid treatments contain 20% polyhexamethylene biguanide (PHMB). PHMB is a synthetic, positively-charged polymer (long chain of repeated molecular units) with a number of notable attributes, including the ability to attach to bacteria and break it apart.
PHMB sanitizers are also known to have a long shelf life, are easy on the eyes and skin, are stable in sunlight and at elevated spa temperatures, are completely soluble in water, have little effect on water balance, and will form microscopic impurities into clumps that are then large enough to be filtered out.
Because a biguanide pool is chlorine-free, that means there are also no chloramines — those smelly, irritating chlorine byproducts that are responsible for red eyes, itchy skin and damaged hair. Chemical costs for a pool or spa treated with biguanide can be significantly higher than those treated with chlorine.
Shopping Considerations
PHMB sanitizers are just one part of a treatment program that also includes an oxidizer (hydrogen peroxide) and for pools, a quat or polyquat algaecide. A manufacturer's program can also include a stain control treatment, a mold killer, a "waterline control" product (for spas), as well as a filter cleaner.
These products bring to light four common problems that can be encountered with biguanide use: increased metal-staining potential, slime/water mold formation in plumbing and filtration systems, a waterline ring in hot tubs, and filters that clog up faster.
It’s also important to note that biguanide products are not compatible with chlorine, bromine, copper algaecides, potassium monopersulfate shocks, copper/silver ionizers, saltwater chlorine generators, and some metal removers and sequestering agents. Regarding the use of PHMB sanitizers with ozone systems, the Pool and Hot Tub Alliance (PHTA) guidelines vary for pools and spas and whether they are residential or commercial applications.* Refer to the manufacturers’ recommendations and talk to a local pool retailer or pool professional for guidance.
Testing Options
PHTA guidelines for water chemistry recommend keeping the biguanide level between 30 to 50 ppm. Taylor offers a stand-alone test kit for testing hydrogen peroxide (K-1443, 2 oz. reagents), and one for biguanide (K-1444, .75 oz. reagents), a combo kit with both biguanide and hydrogen peroxide tests (K-1725, all 2 oz. reagents except for one indicator), and a low-range quat/polyquat algaecide test kit (K-9065, 2 oz. reagents).
All are simple drop-count titrations, meaning the readings are taken at the point the treated sample changes from one color to another. Multiply the number of drops used to reach this endpoint by the equivalence factor provided in the test instructions. For example, in the biguanide test, 1 drop equals 5 ppm of any brand containing 20% PHMB. Taylor also offers colorimeter test kits for biguanide (K-8040) and hydrogen peroxide (K-8020).
*PHTA Tech Notes, BIGUANIDE and OZONE GENERATING SYSTEMS: THE FACTS