Plaster Pool Stains

Years after the start-up is finished, changing water conditions can still damage and stain plaster in some surprising ways.

Gary Gripp’s story begins like so many others.

“I’d been servicing pools in this area for over 15 years when it happened,” says the service manager at Anderson Poolworks in Portland, Ore. Gripp and his team had been hired to drain, clean and refill a gunite pool, and everything seemed to have gone right. “When we left the job site, that plaster was clean as new, and the water was sparkling clear,” he says.

But the next afternoon, the customer called again, complaining that the pool’s water was grayish.

Gripp was hurrying back to the job site when he answered another call from the same customer, the water had now turned a pale shade of lavender.

“And by the next day,” he says, “the water was this beautiful deep purple — like a jewel. I wouldn’t have even guessed water could turn that color.”

The culprit, Gripp discovered, was manganese, a metal known to lend a distinctive range of tints to water: Grayish at lower concentrations, up through brighter shades of purple at higher ones. The real question was, why had manganese suddenly become such a problem for this pool?

“When we tested the fill water, we found that the manganese levels coming out of the tap were just about off the scale,” Gripp says. Luckily, he’d managed to pinpoint the problem before the manganese stained the plaster, and was able to bring the water back into balance with a sequestering agent.

Still, Gripp says he learned something crucial from the experience. “No matter how long I’ve been working on a pool,” he says, “I don’t assume anything anymore. I test the fill water on every visit, sometimes even multiple times. Your chemistry could be perfect, but until you test your makeup water you never know what it could be depositing into the system.”

As builders and service technicians around the country have confirmed, balanced water chemistry is a science — and, in its own way, an art — that reaches well beyond the start-up. Even years down the road, calcium hardness, total alkalinity, pH and other factors can shift dramatically, sometimes in a single day.

Even so, a little preparation and a lot of thoroughness can help stop these problems before they damage the plaster.

Chemical crawl


Changing water chemistry can seem to sneak up on you. Its effects, however, are often — though not always — the results of conditions that have been building up for some time.

Take metals, for example: Their level in the water can gradually rise due to a variety of factors. In dry or windy areas, evaporation removes water but leaves dissolved solids (including metals) behind, significantly raising the water’s total dissolved solids over time. If someone’s been adding a copper algaecide without testing the level regularly, the water’s copper level can rise even more quickly.

Metal deposits inside pipes can be harder to detect, and they often accumulate for years before leading to a problem. “At every pool I’ve seen that’s been around for a few years,” Gripp says, “you can cut a pipe open — even a PVC pipe — and see a deposit of some kind in there. It may be clear and slick, but something always accumulates.”

Most pool water contains some amount of dissolved metals, but these are typically harmless, and invisible to the naked eye. Nevertheless, a variety of common chemical reactions — such as the breakdown of hypochlorous acid under UV radiation and the electrolysis of saltwater in a chlorine generator — increase the water’s concentration of “free” oxygen, the form necessary for oxidation to occur.

The more free oxygen that becomes available, the more metals in the water begin to oxidize — that is, they bond with the free oxygen, which converts them into oxides. Oxidization causes the metals to precipitate out (or fall out) of solution and become visible as a tint in the water. The longer this oxidation reaction is allowed to continue, the greater the risk that the metal oxide will stain the plaster — and eventually be absorbed by its surface.

This is most common with copper, particularly in areas that experience severe storms or droughts, like the Gulf states, says Jana Auringer, owner of The Pool Lady in Coppell, Texas. Auringer travels the Southwest as a consultant, tracking down the sources of plaster stains. She says copper’s telltale pale green tint often appears in pools that experienced no staining issues prior to a bout of harsh weather, and it’s usually traceable to a chemical change in the pool’s fill water.

“[After a storm or drought], we’re finding higher levels of copper in the source water when we test it,” she says. “A lot of times, though, the metal won’t show up on water tests, because it’s already precipitated out and stained the plaster.”

Sudden shifts


Stains and other plaster issues don’t always sneak up so gradually, though. As Gripp discovered with his purple pool, water’s composition can seem to change dramatically in just a few days. Sometimes, water whose chemistry has remained stable for years will suddenly display a sharp drop in calcium hardness or total alkalinity. In those cases, servicepeople say, it’s probably not the same water at all.

Across the country, builders and service pros confirm that municipal water circulation has become more complex over the past few years. These days, the water that flows from a tap is a mixture of water from wells, rivers, reservoirs and storage tanks, and the proportion of water drawn from each source may vary from day to day.

Lance Sada became so frustrated by the seemingly random water chemistry he encountered on his route that he performed his own chemical survey. Using a series of brand-new test kits, the owner of A Clear Choice Pool and Spa Service in Sun City, Calif., tested the water up and down residential blocks in his area. “I found that from one street to another, the water’s calcium hardness might be as low as 20 ppm, or as high as 200,” he says. “Sometimes, the hardness from a single tap varied by 100 ppm from one day to the next.”

In cases like these, the most effective way to prevent problems is to test the pool’s fill water on every visit, before adding any chemicals. But in other situations, the source water itself is less of a problem than what it dredges up.

“Some customers get an accumulation of metal deposits in the bottom of their well,” Gripp says. “When you kick that well on, an abundance of iron, copper, manganese — whatever accumulated in that well source — will come flying into the pool during the initial burst of water.”

Pools that sit idle for the winter tend to display similar symptoms when the weather heats up. “If you shut a pool down for a period of time and you don’t empty the chlorinator, or run the chlorine off beforehand,” Gripp says, “that chlorine’s chewing away at the copper or iron inside the pipes.” When you turn such a system on, it may kick a cloud of metal oxides into the water, and create stains on the plaster.

Perhaps strangest of all, some stains only appear after a plaster surface has been freshly cleaned. “A degraded surface sometimes doesn’t attract stains because it’s so heavily scaled, or has some type of mineral coating on it,” Gripp explains. “And when you resurface it, you might find that your water chemistry looks fine, but all of a sudden you get a stain around the return.” Those stains are most likely metal oxides, to which the plaster’s exposed surface is suddenly vulnerable.

Even if you’re anticipating unpleasant surprises like these, they can’t always be avoided. If you start investigating as soon as you notice discoloration, though, it’s often possible to prevent a metal oxide from becoming a permanent plaster stain.

Getting proactive


Diagnosing the source of a discoloration takes a lot more than educated guesswork. Each pool’s chemical conditions are unique. Manganese, for instance, can appear as a gray, black, lavender or purple stain, depending on the chemistry of the surrounding water. A high TDS reading may point to an excessive level of contaminants, or it might mean you’re adding too much of a particular chemical — or any number of other issues. That’s why it’s crucial to pinpoint the problem’s origin, then confirm it with multiple tests, before you start any treatment.

To become a master of plaster problem-solving, you’ll need to focus on two related skills: Investigating all factors that affect the system, and confirming test results before starting to treat the issue.

The first skill, though it might seem overwhelming at first, is mostly a matter of knowing what questions to ask the customer, and listening carefully to the answers.

“You’ll need to get some background on when the owner first started seeing the discoloration,” Auringer says. “Was it after a heavy rain? After shocking the pool? After a new type of algae treatment? Try to find some change in circumstances to tie the problem to.”

It may also be helpful to find out if any equipment has been replaced, and ask to see the house’s plumbing to check if water has been running through old copper or iron piping. It’s also important to understand the history of the pool’s maintenance regimen, who’s been working on the pool, and what’s been added to the water over time. This can often lead to surprising (and useful) answers.

“It might sound like a lot,” Gripp says, “but if you take every pool on a case-by-case basis, you can find out everything you need to know in a 10-minute conversation.”

The second skill is also somewhat of a matter of instinct, but it too can be boiled down to some basic principles. Techs agree that you’re doing yourself a favor by testing on every visit, in more than one spot in the pool, and by testing source water regularly.

“Always start with a clean slate, and test the tap water first,” Gripp says. In fact, the first time he visits a site, he runs through every single test in his kit. “We also use the separate tests for manganese, iron, copper, phosphates and — if it’s applicable — salinity,” he adds.

Testing the water at several spots around the pool, then averaging the results, can help prevent inaccurate readings due to dead spots or other circulation problems. “Every time I’ve tested multiple spots in a pool,” Gripp explains, “there are significant pH, alkalinity and chlorine differences between them.”

Garrett and Gripp both recommend holding onto your results from the source water, and comparing them against your test results from around the pool for confirmation. “When you go to the doctor,” Garrett says, “he’s always going to check your blood pressure, pulse, temperature and so on, because that gives him a baseline reading to know if there’s anything else wrong with you. It’s no different for pool chemistry: You need to establish a baseline before you know what you need to adjust.”

Finally, before acting on your test results, it’s important to confirm them with other testing methods. At the very least, your test kit should be calibrated against a set of chemical standards, which are usually sold by the kit’s manufacturer. You can also ensure the accuracy of your results by confirming them against another type of test, such as an electronic meter or test strip.

“And that makes you so much more confident when you speak to the homeowner,” Gripp says, “because you can show them the results of multiple tests that all confirm each other.”

Source: Ben Thomas- Pool and Spa News | 2.11.2011

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