Chemical testing is simply the process to obtain chemical results so you can determine if a chemical level is low, ideal, or high. Chemical testing will ensure that you have the information you need to monitor and adjust chemicals so that you can continually maintain optimal water chemistry. Too many pool owners do not test their chemical levels enough; not coincidentally, these are the same pool owners that are most often have to troubleshoot and remedy water clarity problems.
To test the pool chemicals, you have your choice between test strips and a test kit (recommended). That said, you can also use digital testing equipment.
The use of test strips is the most common method for testing pool chemicals. A test strip is a paper strip that contains certain dyes, which will change color once added to your pool water. These colors will correlate with a color chart on the bottle, which will show if a chemical level is low, ideal, or high.
The use of a suitable test kit is the recommended method for testing pool chemicals. A test kit utilizes a test block (which is a device that holds the sample of pool water for comparison purposes during the given tests) and a test compound (which can either be reagents [dyes] or powder or tablets) to actually perform the tests; some tests will use a combination of test compounds. Regardless of what is used for the test, once added, the mixture of the pool water with test compound (either the reagent or powder or tablet) will create a color that will correlate to the color chart imbedded on the test block, which will show if a chemical level is low, ideal, or high. Some test kits are very basic – they will only test your chosen sanitizer (chlorine or bromine) and also the pH level; some expanded - yet still fairly basic - test kits will also test the Alkalinity level. The best test kits will test your sanitizer (chlorine or bromine), the pH, variations of the pH [low or high], the Alkalinity, and the Hardness level; they will also test the Cyanuric Acid level for those of you using chlorine (or salt) to sanitize your pool. If you are going to buy a test kit - which is the recommendation- then buy a complete test kit.
A digital tester is a battery-operated device that will electronically display various test variables. There are digital tests that test for single variables or multiple variables.
You can read the Pool Manual for additional information about testing pool chemicals, how to use test strips, how to use test kits, how to use digital testers, and when to test the chemicals.