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    Credit: NICK ORABOVIC

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    Credit: NATURAL CHEMISTRY

    In some cases, a stain may have spread throughout much of the pool, and may also affect the water’s tint, as in the picture at left. In a situation such as this, it may seem difficult to pinpoint the stain to a specific source — but a careful inspection will usually reveal that it’s more concentrated in some areas of the pool than in others. And, as can be seen in the picture to the right, even a filthy shell often has a pristine surface hiding beneath its grime.

The sudden appearance of a stain or other surface discoloration often brings a barrage of questions, both from the homeowner and the service professional: What caused it? Can it be removed? Can it be prevented from returning? And of course, the ever-popular, “Whose fault is it?”

Thanks to the experiences of veterans in stain analysis and removal, pool professionals now have access to a wide range of time-tested techniques for accurately diagnosing stains, removing them, and preventing their return. In short, successful stain treatment doesn’t need to be a mystery — it’s simply a matter of applying the right tool to the right job.

Here, experts in staining and discoloration walk step-by-step through their strategies for figuring out the cause of a blemish, and ensuring that it’s banished for good.

Search the scene

Stain experts agree that a common mistake is assuming too much before they arrive on site. Staining and discoloration have a variety of causes, from residual minerals to improper water chemistry to poor plaster workmanship — so the search for a culprit is best begun with open eyes and an open mind.

“The first thing I do when I arrive on site is to walk around the perimeter of the pool, looking for staining in certain areas,” says Danny Cervantez, a business development representative for PoolCorp who is based in Van Nuys, Calif. If staining is concentrated around the return line, it’s possible that the water is picking up impurities from within the circulation system. If stains have settled on the bottom of the pool, on the other hand, the impurities are more likely to originate from the fill water itself.

Now is an ideal time to ask the homeowner or site operator a few standard questions about the stains: When did they first appear? Are they more apparent at any particular time of day, or under any particular weather conditions? (Some stains only become visible in the shade.) Have the homeowners recently added or repaired any equipment? Have they noticed any other unusual changes in their water? Sometimes questions like these reveal little in the way of new information — but once in a while, they turn up a clue that’s vital to solving the case.

Sketch the shape of the pool on a notepad, and make careful notes of the locations and distinguishing features of any stains. Note any surrounding trees, dirt piles, copper pipes or other potential stain contributors.

Another useful investigative technique is to look for other areas to which the stains have spread. Discoloration found only on the pool’s plaster may be the result of flawed workmanship — for example, an improper startup, over-troweled plaster or improperly mixed pigments — but if the stains have spread to the grout, and to an unattached vessel such as a spa or waterfeature, they’re most likely the result of residual metals or improper water chemistry.

It’s also important to pay attention to the stains’ color. While most metal stains will exhibit a variety of different colors depending on various chemical factors in the water, some telltale clues — the blue of copper, the brown of iron and the yellowish-tan of manganese — can point an investigation in the right direction. Colored water may also be an indicator of metals, which are likely to plate out onto surfaces as they oxidize.

Even so, colors are, at best, only a very general indicator of a stain’s cause. To pinpoint the problem further, it’s critical to test both the fill water and the water in the vessel using multiple testing methods — e.g., a titration-based kit, test strips and an electronic meter — to ensure that the results are as accurate as possible.

“I go to every job site armed with a test kit, electronic meters and test strips,” Cervantez says. Using these testing methods, analyze samples of both the fill water and the water in the pool — then compare those results against one another to get a clearer idea of how those two chemical solutions are interacting to produce the conditions in the pool.

To ensure accuracy in testing, it’s vital to keep test kits properly calibrated against chemical standards of known composition (available from many test kit manufacturers). “A lot of guys think they can just keep using one old test kit until the solutions run out,” Cervantez says, “but you’ve got to calibrate your kit regularly, and confirm your results through multiple testing methods.”

Examine the evidence

The next step is to perform a more in-depth investigation of the stains themselves. Keeping the stains’ location and color in mind as general diagnostic guidelines, examine them close-up from a variety of angles. Look for any telltale shapes or markings that might reflect an object that fell into the pool, or a misused tool.

“If the discoloration is due to overworked plaster, you can often see, at the edge of the discoloration, the outline of the trowel that’s been passed over the same spot too many times,” says Chris Marcano, director of training and education for Natural Chemistry in New York. Metal staining, meanwhile, often takes a smooth-edged shape, while algae stains typically exhibit more ragged edges.

Beyond these general traits, stains of certain shapes can point to a specific source. For example, “you can look for little ‘starburst’ or ‘butterfly’ stains right at the waterline,” says Ron Gee, warranty manager at CDC Pools Inc. in Chandler, Ariz. “Those little encrustations are due to low carbonate alkalinity.” By a similar token, small dotted stains on an aggregate surface may point to metals or mineral compounds leaching out of the aggregate and depositing atop the outer layer.

In some cases, organic materials — blown into the pool or present in the mix — may also leach out and create small discolored spots. For example, blossoms or leaves may have blown into the pool during the plastering process, or abalone or mussel shells used for decorative purposes may, in rare cases, break down and form small discolored spots on surfaces.

If possible, reach into the water and feel the stains for any distinguishing physical characteristics. “I investigated one pool where the stain itself was bluish and smooth, and all the area around it was rough,” Cervantez says. “That told me that the fill water was corrosive, but the pool water was leaving scale deposits.”

Another field-tested tactic is to diagnose the stain by attempting to treat it: Rub a chewable Vitamin C tablet against the stained area, or — if the area’s out of reach — drop the tablet onto the stain and let it sit for a few minutes. If the stain is metallic in nature, the ascorbic acid in the tablet will displace those metals from the pool’s surface and put them back into solution. This technique doesn’t remove the stain for good; it simply moves the metal from the surface to the water, where it can be filtered out with the help of a chelating or sequestering agent. Even so, it’s an effective way of diagnosing a stain caused by metal impurities.

Though all these signs can help pinpoint the source of a stain, it’s crucial to consider them through the lens of verified water test results. Only a proper chemical analysis can confirm a stain’s cause for certain.

Choose a treatment

Once the cause of the stain has been isolated and confirmed, it’s time to present all the evidence to the customer and suggest a course of action. Be prepared to deal with counter-arguments at this point — especially if existing equipment or customer negligence is a cause of the problem. If this situation arises, listen carefully to any objections the customer offers, then calmly present the evidence from various test methods, as well as careful observation of the scene. As with any investigation, the more thorough the documentation, the more effective the case.

The treatment itself is often a comparatively simple process — many companies make stain removal chemicals and kits, and a clear understanding of the stain’s cause will simplify selecting the right product. If the discoloration turns out to be a result of improper plaster workmanship, however, the solution may not be so straightforward — it may be necessary to call in a specialized torch team, or (in extreme cases) to sand and replaster the shell. Again, a well-documented case will smooth customer negotiations considerably.

Once the treatment is under way, the most important consideration is protecting the pool from a relapse. “You have to have the thought process that metal is going to get back into that pool at some point,” Marcano says. “It may come from the source water, from the equipment or from some other cause — but it’s very rare to see a pool that gets one stain and never gets stained again.”

Still, it’s possible to prevent many future stains — and quickly remove any that do occur — by taking a proactive approach to water chemistry and maintenance. If metals are getting into the pool from the fill water, discuss the option of installing an in-line filter capable of removing metals, or keeping a higher level of sequestrant in the water.

It’s also vital to balance the water’s chemical parameters — pH, total alkalinity and calcium hardness — into the ranges recommended as ideal by groups such as the Independent Pool & Spa Service Association and the Association of Pool & Spa Professionals (this information is available for free on these groups’ Websites), and talk with the customer about the importance of keeping the water balanced.

Through vigilant water testing, careful investigation and clear customer communication, it’s possible to prevent many future stains from taking hold. But even for pools that offer new stain surprises, a well-honed sleuthing process can turn a headache into an opportunity to impress customers — and gain new ones.