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Most pool owners assess the well being of their swimming pool by what they can see: the clarity of the water and the appearance of its surfaces. As a service technician, you must be able to diagnose problems that can compromise the homeowners’ visual evaluation of their vessel. There are many common issues that lead to staining in pools, and a few not-so-well-known offenders.

Water balance

Most stains and discoloration can be traced to improperly balanced water. But even “perfectly balanced” pools have the potential to contribute to these types of problems due to the almost-daily influx of metals, minerals and other contaminants. Oxidation also is a concern.

Common organic staining scenarios

Staining and discoloration can be broken down into two main categories: organic and inorganic. Common organic causes include scale, algae, “pink slime,” white water mold and vinyl liner mold. The Langelier Saturation Index measures the corrosiveness and neutrality, or scaling ability, of water. Water, by nature, “wants” to be neutral or balanced. When pH and/or total alkalinity are high, water cannot rid itself of either of these two important components, but it can push out calcium. Scaling is one unwanted by-product of this reaction.

When heavy rains combine with hot weather and low or no sanitizer, algae in its many forms can become an issue. Mustard algae seems to vanish easily when brushed, but will reappear quickly and continue to spread if left unchecked. Black algae creates a protective gelatinous coating. It also has roots, which can penetrate a pool’s plaster, fiberglass or vinyl surfaces. Green algae can first appear as a tinting of the water, which can rapidly transform a pool into a veritable swamp if not treated. In addition to a discoloration of the water, green algae also can produce rapidly spreading stains throughout a vessel.

Pink slime actually is reddish bacteria that most of us have seen on our showerheads. It can be introduced by rain, soil and contaminated swimsuits — as can mustard algae — and can rapidly grow in circulation pipes. Like pink slime, white water mold grows in circulation piping. This contaminant resembles small floating pieces of white tissue by the time it finds its way to the pool water. Although not a surface stain, vinyl liner mold is a fungus that grows underneath a vinyl liner, which is visible as a shadow beneath its surface. Tannins, commonly associated with trees, also can find their way into pools and create staining.

Common inorganic stains and discoloration

Inorganic troublemakers include scum-line buildup, cloudy or tinted water and iron and copper stains. When suntan lotions, body oils, make-up and dirt gather at the waterline, an unsightly scum-line buildup can occur. It should be noted that organic contaminants also can contribute, though they aren’t the main culprits. If left unchecked, additional dirt and contaminants will more easily adhere to an existing scum line, creating a snowball effect.

Cloudy water is a byproduct of unbalanced water, poor circulation and poor filtration. Ironically, the response of then adding too much clarifier can worsen existing cloudiness.

Metals such as iron, copper and manganese can produce a tinting of pool water and serve as a warning of sorts that metals are present in the system. All it may take is a shock treatment to plate the metals from the water onto a pool’s surface, thus creating a metal stain. Metal stains can also potentially be introduced from well and municipal water, metallic equipment parts, pool chemicals such copper- and silver-based algaecides, certain grades of salt for chlorine generators, certain grades of chlorine, ionizers, lawn chemicals and more.

Lesser-known causes of staining

Copper cyanurate, dubbed “purple haze,” can occur when a high stabilizer level (above 100 ppm) combines with copper, creating a purple precipitant. This purple stain is bright and highly visible, often showing up on tile, spillways and pool cleaners. If left untreated, copper cyanurate eventually will adhere to all pool surfaces. Until the stabilizer level is lowered to below 70 ppm, the problem can appear to be chronic.

Another potential stain-causer: potassium permanganate. If a house’s water supply is high in iron, manganese or hydrogen sulfide, many homeowners choose an iron/hydrogen sulfide reduction filter for their water treatment system. This filter contains manganese green sand, which reduces contaminants through an oxidation/filtration process. Should green sand water mix with make-up water, it can contribute to staining. The manganese in the filter is expelled when the system recycles, and it will create a pink/purple potassium permanganate stain when it comes in contact with the pool finish.

Iron and scale are two common causes of staining in a pool, but occasionally they work together to create a more obscure form of discoloration. This hybrid stain, known as iron scale, can be particularly difficult to remove, as standard treatment doesn’t often work. The only way to alleviate this buildup of layers is to remove first the top layer of scale, then treat the iron stain that it previously covered.