By Chris Marcano
Now that the long winter is finally coming to an end, homeowners are getting ready to pull off their pool covers and get their backgrounds ready for summer fun. That said, one of the strangest experiences for all homeowners is opening the pool to discover a purple crystal-like stain on the water surface. Service professionals have known about this phenomenon for years and commonly refer to it as the ‘purple haze.’
What causes a purple stain?
Contrary to popular belief, the purple haze is not an organic bacteria or algae issue. It is actually the result of improperly balanced water chemistry combined with a mineral issue. This purple stain is caused by copper cyanurate, which occurs when excessive levels of cyanuric acid (CYA) combine with non-chelated copper (high-quality copper algaecides are chelated, which means they are protected against staining pool surfaces) present in the water. This problem is most common in pools that have cyanuric acid levels measuring above 100 parts per million (ppm).
A previously rare phenomenon, the purple haze seems to be on the increase these days. The use of cheaper, lower-quality copper algaecides at pool closing appears to be a major reason for the spike.
Ironically, colder water aids the reaction between copper and cyanuric acid to form these purple crystals. Copper cyanurate cannot be easily scraped, scrubbed, or removed.
Dealing with a purple pool
Adequate measures must be taken if one encounters a purple pool. The first step is to lower the CYA level of the pool water to around 30 ppm by performing a partial drain and refill. When cyanuric acid levels are lowered, copper levels in the pool are also reduced—as long as the source water does not contain copper. This is a good time to add a non‐phosphate metal control product to deal with the copper that still remains. Once the CYA levels are in line, adjustments need to be made to the pool water’s pH and total alkalinity.
Note: Regular stain removal procedures may remove the pigmentation, but it typically requires three times the normal amount of traditional stain removal chemicals and a lot of time.
Prevention is better than cure
Prevention is truly the preferred method of dealing with the purple haze. The first step is keeping CYA levels below 100 ppm (and ideally in the recommended 30 to 50 ppm range). Service professionals should also consider reducing the amount of stabilized chlorine during the pool season if they tend to see cyanuric acid levels are on the higher side. The best way to do this is by using alternative shocking products, such as calcium hypochlorite or liquid chlorine, which will prevent the stabilizer level from increasing.
Copper algaecide can be a fantastic product to prevent algae formation—when it is properly formulated. However, one must avoid using inexpensive versions of these products at pool closing.
It is important service professionals work with an aquatic product catalogue or distributor that sells copper algaecides designed to provide protection against unintended staining, such as copper cyanurate. Cheaper copper-based algaecides are nothing more than stains waiting to happen.
Chris Marcano is the national account director for KIK Custom Products, a manufacturer of pool and hot tub chemicals as well as detergent, automotive, and personal care product categories. Marcano has more than 19 years of experience in the industry and is a Certified Pool/Spa Operator (CPO) instructor, and a member of the education committee for the National Plasterers Council (NPC). He is also active on the Pool & Hot Tub Alliance (PHTA’s) board of regents and is a local PHTA chapter president. He can be reached via email at firstname.lastname@example.org.