Water Test Kits
PH is most often tested with phenol red, a reagent that turns darker with higher pH. Phenol red gives a false reading (or sometimes no reading) for a pH below 6.8 or above 8.2. High chlorine or bromine levels may cause interference, so most manufacturers include a chlorine neutralizer with the test. Also, pH can be tested with an electronic pH meter, which is much more accurate than a reagent test.
Testing Methods
Color comparison - a reagent is added to water, and the resultant color is compared with a test strip. Another variation is a test strip that is dipped in the water, then compared against a standard set of colors. This can be done by adding the water to a plastic container called a "color comparator," which has a set of standard colors printed on its sides; or by dipping a test strip in the water, then comparing it against a set of standard colors on the bottle. Chlorine and pH are commonly tested in this way.
Drop-count - also known as a "titration" or "titrametric" test. A reagent is added to a water sample, and the color is checked against a standard set of colors. Then, more reagent is added drop-by-drop, until the liquid changes to another color or turns clear. As many as three different reagents may be involved in this process: for instance, one may adjust the pH, while the other two produce color reactions. These tests are common for measuring hardness and alkalinity
Electronic testing, sometimes known as "electrometric" testing, takes advantage of the varying electrical conductivity of different compositions of water. The most common electronic tests areTDS meters, pH meters, and ORP electrodes. These tests do not require a reagent, and but may take hours to develop an accurate reading
