The National Pool Industry Research Center has released the results of its study of pool and spa test kits.

The research, completed in March 2007, examined 14 products from seven manufacturers and tested them against a laboratory value and precision between multiple readings.

Participating firms included AquaChek, Guardex/BioLab, LaMotte, Pentair Water Pool and Spa, Jack?s Magic Products and Palintest USA. Tests were administered by NPIRC researchers and teams at six universities.

The two most notable trends among the test kits are the tendencies to underestimate chlorine and overestimate calcium hardness. On average, kits produced a chlorine reading 30 percent lower 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.

The drop size can introduce another variable because the tips of bottles can become charged, creating a small drop, Seechuk added.

The subjective nature of colorimetric tests also could have contributed to result variances.

?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.?

NPIRC was established in 2003 to research issues affecting the aquatics industry. The group is funded primarily by the National Plasterers Council.