The Purple Haze
Be Ready for Pool Season
By Chris Marcano
Now that winter is past, recreational swimming pools are pulling off their covers and getting those pools ready for summer fun. However, one of the strangest experiences for aquatic facility managers is the discovery of a purple, crystal-like stain on the surface. Service professionals have known about this phenomenon for years, and commonly refer to it as the "Purple Haze."
The purple haze is not, contrary to popular belief, an organic bacteria or an algae issue. The problem is actually the result of improperly balanced water chemistry combined with a mineral issue. The purple staining is caused when the pool water has formed something called copper cyanurate.
Copper cyanurate occurs when excessive levels of cyanuric acid combine with non-chelated copper that is present in the water. This problem is most common in pools that have cyanuric acid levels measuring above 100ppm.
This previously rare phenomenon seems to be on the increase these days. The use of cheaper, lower quality copper algaecides (which are typically sold at mass merchants) at pool closing appears to be a major reason for the spike.
Ironically, colder water like we have in the spring aids the reaction between the copper and cyanuric acid to form these purple crystals. Copper cyanurate is not easily scraped, scrubbed or removed.
Dealing with a Purple Pool
If you do have to deal with a purple pool, there are steps to correct the problem. The first step is to lower the cyanuric acid level of the pool water to around 30ppm by performing a partial drain and refill. It is extremely important to follow the advice from a trusted pool professional for this step. When you lower the CYA levels by partially draining and refilling, you also happen to be reducing the copper levels in the water, as long as your 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.
It is possible, through normal stain removal procedures, to eventually remove the stains, but typically it requires three times the normal amount of traditional stain removal chemicals and a lot of time.
The 3 Ps—Prevent Purple Pool
Prevention is truly the preferred method for dealing with the purple haze.
Keeping the cyanuric acid levels below 100ppm (and ideally in the recommended 30-50ppm range) is the first step of prevention you should consider.
You should also consider reducing the amount of stabilized chlorine that you use during the pool season if you tend to see your cyanuric acid levels end up on the higher side. The best way to do this is by using alternative shocking products that will not increase your stabilizer level such as calcium hypochlorite or liquid chlorine.
Avoiding the use of inexpensive copper algaecides at closing is also a must. Copper algaecide is a fantastic off-season algae prevention product when it is properly formulated. If you are encountering this problem because someone in your organization used a lesser grade copper algaecide, remind them of the importance of working with an aquatic catalog or distributor that sells copper algaecides that are designed to provide protection against unintended staining like copper cyanurate. It's important to remember that some mass merchant copper-based algaecides are nothing more than stains waiting to happen. Stick with products designed for recreational aquatic facilities so you can avoid the purple haze.
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