The second debate pertains to the most significant source of phosphates in swimming pool water. Again, let’s separate some facts from myths. First of all, unless you live in an older city such as New York, Chicago, or St.Louis, less than 15% of municipal cities still add polyphosphates (SHMP) to reduce pipe corrosion.Second, most water samples collected from California to Florida revealed that many source waters contain only 20 to 100 ppb phosphates. For example, and to the surprise of many, Phoenix metro water contains only 50 ppb PO4 (spectrophotometer analysis). Regarding fertilizer phosphate contamination, one pound of fertilizer containing 10% phosphorous would add 600 ppb PO4. Although this is high, one pound of fertilizer added to a pool is highly unlikely. Last but not least, since phosphates do not atomize into the atmosphere, rain water is not a source of phosphates – period. The debate further states that soil, dust, and organic debris are also a large source of phosphates in pool water.To test this theory, another rather simple experiment was conducted. Soil samples were collected from vineyards in the San Joaquin Valley( the largest agricultural producing county in the world).Two
large 2000 ml beakers were filled with distilled water–without PO4.The proportional equivalent of 100 and 500 pounds of soil were added to each beaker to replicate similar amounts that would have been added to a 20,000 gallon pool. Each beaker was agitated to allow absorption of phosphorus from soil into the water. After adequate contact time, analysis of each sample revealed: the 100-pound soil equivalent sample beaker only released~800 ppb of phosphorous and the 500-pound soil equivalent sample beaker tested to contain only~3500 ppb of phosphorous. While these levels of PO4 may seem high, we actually expected a much higher level of PO4(such as 10,000–30,000 ppb) considering the large amounts of phosphate-rich soil used.Our conclusion: wind-blown dirt and organic debris cannot be a significant source of phosphates in normal pool water because the amount of dirt required to achieve high levels of PO4 would be unrealistic in a normal pool environment.
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So you ask, what is the principal source of phosphates in pool water? The answer appears to be pointed at an earlier claim – scale and stain products. These products are widely used for stain lifting, startups, saltcell descaling, and general scale control. Many products were tested. Most products contained a phosphonic acid. A typical 20% formulationtested releases about 1500 ppb phosphates and the most concentrated product releases over 4000 ppb into chlorinated pool water after about seven days. A word of caution,a few scale and stain products claim to be a “no phosphate” formula and were tested to the contrary; however, there are several scale and stain products that do not contain phosphates.
In final conclusion, there is no evidence to support increased algae growth rates in swimming pool water below 1000 ppb. The largest source of pool phosphates appears to be from scale and stain products and not environmental. In the last few years, the use of phosphates in consumer and commercial products has sharply declined especially due to costs which nearly jumped 775% in 2008.
Recommendation: take phosphates out of pool water when they exceed 1000 ppb (300 ppb is a sufficient reduction level), use a low or non-phosphate scale – stain product, maintain adequate chlorine levels,keep pool water pH within proper range, and use an algaecide especially for pools with persistent algae blooms.
P.S.: To reduce the high cost of removing phosphates, test and treat for phosphates annually, stop worrying about them, and instead go back to the basics to keep treatment costs under control.
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