The National Pool Industry Research Center in San Luis Obispo, Calif., has released the results of its study on the accuracy of pool and spa test kits.
The study examined 14 products from seven manufacturers, testing them for accuracy against a laboratory value. The project also looked at the variance between readings using the same kit. Participating companies included AquaChek, Guardex/BioLab, LaMotte, Pentair Water Pool and Spa, Jack’s Magic, Palintest and one anonymous manufacturer.
Tests were administered by a traveling NPIRC research group, as well as teams at six universities. The study was completed in March 2007.
The two most notable trends among the test kits were a tendency to underestimate chlorine and overestimate calcium hardness. On average, the kits produced readings of 30 percent lower total chlorine than the laboratory test. The average difference in calcium hardness was nearly 40 percent.
However, human error may play a role in these discrepancies.
“Every test company I know says [there’s] a 10 percent variability because it’s a field kit,” said Tom Seechuk, industrial products marketing manager at LaMotte Co. in Chestertown, Md. “You’re not going to fill the line up right or you’re not going to hold the reagent bottle correctly.”
The drop size can introduce another variable because the tips of bottles can become charged, creating a smaller drop, Seechuk added.
The subjective nature of colorimetric tests also may have contributed to the variance of the results.
As expected, the photometer from Palintest recorded results with much higher precision, meaning less deviation between the readings.
“Because colorimetric tests are a matter of interpretation, they’re certainly going to be a problem unless you have a colorimeter,” Seechuk said. “But a lot of [service] companies don’t want to spend the money.”
However, even with the seemingly large differences in results, the variances may only account for a difference of 0.1 on the Saturation Index, he noted.
NPIRC was established in 2003 to research issues affecting the pool and spa industry. The group is funded primarily by the National Plasterers Council Research Foundation.