When Pools Turn Purple

Among the most peculiar stains the pool professional will encounter are those created by manganese or copper cyanurate.

Both create a strange purplish hue in the pool, but the latter is especially peculiar.

When water contains copper and a high level of cyanuric acid, the combination creates copper cyanurate. This can reveal itself in the form of purple crystals along the waterline, skimmer basket, walls and bottom.

It’s one of the prettiest chemical imbalances you’ll ever see.

Ray Rescildo, owner of Certified Pool & Spa, in Plymouth, Conn., recalls responding to his first Code Purple. A vinyl liner had a periwinkle tint to it.

“My first thought was that he got a new liner,” Rescildo remembers.

But it was rough to the touch, like sandpaper.

The chemical readings, not surprisingly, went off the charts. That was due to the homeowner’s DIY approach to pool care — using plenty of dichlor shock and stabilizing tablets, which jacked up the cyanuric acid with every application.

Another curious thing about the condition of the water: It was crystal clear. Only the surface of the vessel had the telltale magenta blemish.

Rescildo: “It was so acidic that nothing would grow in it.”

He managed to brush the crud off, and the effect it created when vacuumed was something to behold.

“My discharge hose was literally pumping out a beautiful lavender,” he says.

Dave Goulart’s encounter with the mauve monster was similar, but with one difference: There wasn’t one obvious culprit. The owner of Aqua Hero Pool Service in Livermore, Calif. found that a confluence of factors may have contributed to the grape Kool-Aid-like appearance of the pool.

For one, the mineral sanitation system was on the fritz. Plus, the city’s fill water in that neighborhood tended to run high in metals. Finally, the CYA readings showed well over 100 ppm.

“But we couldn’t get a true reading on it,” Goulart says. “It may very well have been over 300.”

The pH and alkalinity were low. Plus, water hadn’t been changed out in over a decade.

“It was just waiting for that moment to snap, and this was the breaking point,” Goulart says. “Everything that could’ve gone wrong at one moment absolutely did.”

The purple deposits along the surface proved difficult to remove, requiring Goulart to drain the pool and pressure wash the fiberglass vessel. Experts have a theory about this: Fiberglass has a strong magnetic charge, so metals would naturally adhere to the surface.

What Goulart and Rescildo describe is a rare phenomenon commonly referred to as purple haze. Some professionals say this is most likely to occur during spring. It’s an unpleasant surprise when homeowners open their pools for the season. Professionals speculate that cold water may have something to do with the purple grit along the waterline. Indeed, temperature is a factor in the saturation index, so this could very well be the case. However, copper cyanurate can arise in warm pools, too. For instance, Rescildo’s confrontation with the phenomenon happened in July.

But all it really takes for this odd chemical reaction is the presence of non-chelated copper and CYA of 100 ppm or higher.

Some experts believe pools with saltwater systems are more susceptible, because of their potential for galvanic corrosion, the electrochemical process in which one metal corrodes faster than other metals in the presence of an electrolyte.

Corrosion in salt pools could be the source of copper that helps spark copper cyanurate. That’s why experts advise installing a sacrificial anode. This device is made of zinc, which has a more active voltage than other metals, so galvanic corrosion strikes it first, sparing ladders, light rings and other metallic components from degradation. And you don’t have to worry about zinc making any funky deposits. It doesn’t stain.

And as Goulart experienced, mineral systems could contribute to the problem if the pool isn’t properly balanced. Experts warn that copper, which is an effective algaecide, has the potential to stain when it falls out from a combined state to free copper.

At the end of the day, it doesn’t matter what kind of sanitation system the pool is running. All it takes is the combination of copper and exceedingly high levels of CYA to produce a purple pool.

Fortunately, there’s an easy fix.

First, lower the CYA level in the water to between 40 and 50 ppm. To do this, simply perform a partial drain and refill. You may have to do this several times to dilute the CYA to adequate levels. As an added bonus, this process helps lower copper levels, provided the source water isn’t the problem.

With the CYA under control, attack the copper using a metal control product. Then get the pH and total alkalinity in line. The stains should dissipate over time, even in a plaster pool. Some pros fear that purple stains are permanent on a more porous surface. Chemical experts say this isn’t the case. However, the longer the stain sits untreated, the more difficult it can be to remove.

The next step is to ensure copper cyanurate never again rears its pretty purple head. In most cases, the stains occur over a period of time. So keep a keen eye on CYA levels.

Caution your customers against the overuse of stabilizers and copper-based algaecides. And if the neighborhood is known to have heavy metals in the fill water, get the pool on a good preventive maintenance program with a weekly dose of metal sequestering agent.

Since Rescildo eradicated the magenta menace, his customer hasn’t seen a re-occurrence. He properly trained the determined DIY-er. Rescildo recently received this encouraging text message from him: “Knock on wood, the purple monster has not returned … Maybe it’s because I’ve really stayed on top of watching everything this summer.”

His customer noted that the CYA levels are in the low range of 0-30ppm.

“If this was the culprit,” he added, “the culprit isn’t there right now.”

Likewise, Goulart doesn’t anticipate a copper cyanurate sequel: “We’re very strictly monitoring the metal levels.”