Questions & Answers Test Strips Facts
Water analysis can be as easy or as involved as you want it to be. Often we may convince ourselves that the more difficult the water analysis, the more accurate the results. This isn't always the case, however. With new test strip innovations, water analysis has become a task that can be performed by the average person while producing accurate, reliable results under most conditions and demands. The first step in trusting test strips is to become familiar with the answers to frequently asked questions (FAQs) about test strips. The following questions and answers are simple and to the point.
The Basics Question: How do test strips work?
Answer: Test strips are small strips, typically produced from plastic “sticks,” with chemically impregnated pads on the end. These pads are designed to react with specific ions and produce a specific color change. Once a test strip is reacted, and a color is developed, the strip is then compared to a printed color chart. The printed color chart is specifically designed to represent color reactions at various concentrations. Matching the strip to the closest color match produces a concentration reading.
Q: How accurate and reliable are test strips?
A: Test strips can be quite accurate. Most manufacturers utilize several industry-standard reference methods to compare and calibrate their strips. One of the most comprehensive collections of reference methods is contained in the American Water Works Association (AWWA) manual for water and wastewater treatment and evaluation. Once the standard reference method is established, the test strip manufacturer determines the level of accuracy that the strips should meet; generally, the accuracy is within a color block up to the expiration date of the strip. The test strip is put through multiple testing phases and scenarios to see how it performs in real-world situations. After the grueling testing phase, the data are collected and the results are evaluated. If the test strip meets the desired level of performance, it's accepted and ready for distribution. Competent test strip manufacturers will not release a test strip if its performance doesn't meet the highest possible accuracy and reliability.
Q: Can I use a drinking water quality test strip in my pool or spa?
A: Generally, it's recommended that you use a test strip that has been specifically designed to work in the water sample that's being testing. Most test strips are designed to test either drinking water quality or pool and spa water quality. When an incorrect water sample is tested using a water quality test strip, the results can often still be acceptable. As an example, if a water quality free chlorine test strip is used in pool water, the results will more than likely be correct to within a color block. The reason for this is that pool water and drinking water have similar chemical properties. Still, be sure that you are using the right strip for your application to help avoid any inaccurate results. Colorization
Q: How accurate are the test strip color charts?
A: The color charts, supplied with test strips, are the most important factors in getting reliable results. The test strip can be the best available but if the strip pad colors don't match the colors printed, then accuracy suffers. To provide the most accurate color charts available, manufacturers employ tried and true quality control procedures. Beginning with the design work and through the final printing of the color charts, the quality control staff monitors the process. Quality control members also do a 100 percent check of all printed labels before use. Before the test strips are shipped, the labels are checked once again to make sure that the test strip lot and color chart label meet quality control specifications. By employing such a system, test strip manufacturers are able to provide accurate products.
Q: When I use the test strip, I get a color that isn't on the supplied color chart. Why does this happen and what does this mean?
A: Occasionally, a user will get a color that isn't on the chart. When this happens there are several possible explanations. First, the user needs to make sure the directions were followed closely. When manufacturers develop a test strip and write the directions, the times and procedures provided are written in detail for a reason. Often times, a user didn't follow directions closely, which may result in the strip developing an unusual color. Keep in mind that while most test strips look similar, the directions for the strips can be very different. This can be true even when dealing with test strips from the same manufacturer. Second, an unmatchable color can develop if the sample has a certain level that isn't represented on the color chart. When a color chart is developed for a test strip, the manufacturer has to make a couple of choices—what are the common levels encountered in testing for this ion, and what is the separation between the colors, i.e., how distinguishable are the colors from each other. Several different things can cause a color that doesn't match what is on the color chart. Commonly, it can mean that the level you are detecting isn't included on the color chart. Try to extrapolate the concentration of the color for the best estimate. Sometimes when the color doesn't match at all, this can be caused by interference ions in the sample. When this occurs, contact the manufacturer to see if another, more appropriate, test is available.