Expert Pool & Spa, Inc.
"ASK THE EXPERTS!"
Omaha Nebraska
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Expert Pool & Spa, Inc.
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All common water sources contain dissolved metals. The amount varies greatly in different regions of the country and can even very widely in one community. Omaha's water is pretty good right out of the faucet. The pH is about 7.6, alkalinity is about 40-50 ppm and TDS is low. Elkhorn on the other hand, has a very high total alkalinity and very high pH. Most rural private well systems around Omaha have a lot of metals in them and high alkalinity. Metals can cause staining of surfaces and can change the color of pool water to brown, blue, green, gray, or black. Manganese produces a black-brown-purple cast and may not be noticed until extra chlorine is added, or until it is necessary to raise the pH. Copper produces a light blue or green cast to the water. When copper is oxidized and precipitated it can cause turquoise or black surface stains. Iron is common and may be present in water taken from wells or rivers. When oxidized it can turn water clear green, then cloudy yellow going to rust brown. It is recommended that the level of metals in the pool or spa be kept at 0 ppm. Small amounts of metals under 1.0 ppm can be held in suspension and removed by filtration by adding a sequestering agent to remove the metals. Note that in older installations with copper piping, any velocity of water over 10 feet per second will erode copper from the piping and introduce metals into the pool or spa water. POOL SURFACE STAINING Staining is caused by the precipitation of colored metals - the main culprits being copper, iron, and manganese. With the exception of manganese (whose stains are rare in pools), iron and copper cause heavy metal staining as these elements belong to a chemical grouping called "heavy metals" and are composed of high densities of the metallic element. These stains are caused by soluble metals getting into pool water from several sources:
PREVENTION AND REMOVAL OF POOL STAINING Soluble metals can be inhibited from precipitation by sequestering and chelating agents. These are chemical compounds that complex (or bind) with the colored metal ion to keep it in solution. Some of these agents are so strong that they will literally react with the metal compounds that have already precipitated onto the pool wall and pull the metal ion back into solution, thereby removing the stain. Such stain control/removal products are readily available from most chemical manufacturers. Stains on concrete walls are difficult to remove due to the porous nature of the plaster, and require a process called acid washing. Diluted muriatic acid is scrubbed onto, and then flushed from, the pool walls. This process is very effective in removing stains as a thin layer of concrete and the adherent stain is dissolved by the acid. Corrosion and scaling are accelerated by high temperatures of heated water. A temperature rise of about 35ºF will double the rate of corrosion; thus, corrosive conditions are considerably more severe in high temperature areas such as heat exchange tubes on gas heaters. Scale is also more rapidly formed at higher temperatures. Corrosion in the form of localized pitting, cracking, dezincification of certain types of brass, corrosion of crevices under gaskets and o-rings may occur in most water systems. Staining caused by iron, copper, and manganese may appear in the form of tarnishing, discoloration or rusting. In sand filters, excessive scale formation results in channeling and hardening; in DE and cartridge filters, it forms not only on filter elements, but also on filter cloths, plugs the filter and reduces the efficiency of filtration.
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~ Expert Pool & Spa, Inc. ~
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