Pool testing kits come in several different varieties. Test strips are the cheapest and easiest to use. Make sure the strips come with a color chart printed on a card or the back of the bottle so you can interpret the results. Once you own the chart, you can purchase additional bottles of strips rather than whole kits. Another test variety are liquid test kits. You add the included chemicals to the water, then look for color changes. It can be difficult to mix the dye in the proper proportion and spot slight color changes. The last option is a digital water tester. Dip the end in the sample to get results. These are accurate but expensive and can malfunction. After this time, the strip will change colors. Remove the strip immediately, but don't shake off the water. For testing strips, you'll only need a single water sample. When doing a liquid test, pour a few drops of the dye into the water sample. You will need to collect a new sample of pool water for each dye. For digital testers, stick the sensor in the sample. The color chart will be somewhere in your kit or on the back of the bottle of testing strips. If you bought 4 in 1, 5 in 1, or 6 in 1 strips, several colored patches on the strips may change. Each one corresponds to a separate chemical measurement on your color chart. Strips that aren't all in 1 only test a single element. You'll need to go to the store and get separate strips for chlorine, pH, and alkalinity. Strips for cyanuric acid and water hardness are also recommended. Water testing below 7.2 is more acidic, so if you notice colored stains from metal or corroded pipes, low pH could be the culprit. Water above 7.8 is more basic, causing chemical deposits on pool gear and preventing chlorine from killing bacteria and algae. Both high and low pH water irritate eyes and skin. The pH level can be raised by adding soda ash, which is available at any pool store. Follow the directions on the label to figure out the proper amount to add. Lower the pH level by mixing in muriatic acid. Again, the corresponding patch on the testing strip will change colors, so read the chart to determine the chlorine level. Chlorine prevents bacteria and algae, so low chlorine can be the cause of green water or illness. Chlorine is a skin irritant at high levels. If your pool uses bromine instead of chlorine, the color on the strip should correspond to a level between 2.0 and 4.0 ppm. Chlorine tablets are normal ways to raise this measurement. Get them at the store and put one in the chlorinator or skimmer basket every week. Chlorine burns off naturally in the day. You can lower it further by applying a neutralizing chemical like sodium thiosulfate or sodium sulfite. The alkalinity changes a lot due to the pH level, or it can cause the pH level to change. High alkalinity causes scaling and cloudy water, while low alkalinity corrodes and stains pools. Baking soda (sodium bicarbonate) is the main product used for raising the alkalinity level. Muriatic acid or dry acid (sodium bisulfate) are effective for lowering the alkalinity. Cyanuric acid is typically included in chlorine tablets, keeping the chlorine in the water longer. It's an acid, so it can be the reason for lower pH and alkalinity. It's also important for keeping the chlorine level consistent, so a low chlorine level could be caused by a lack of cyanuric acid. Cyanuric acid is added through regular usage of chlorine tablets. Adding a product called stabilizer, found at pool stores, also helps. To lower the cyanuric acid level, stop using chlorine tablets for a while and switch to chlorine shock. For immediate effect, drain some of the water and replace it with untreated water. For vinyl pools, the level needs to be between 175 and 225 ppm. In concrete pools, it's best between 200 and 250 ppm. Water low in calcium abrades pool walls and liners. High calcium levels cause cloudy, scaly water. Chlorine shock is responsible for increasing calcium levels. To lower the calcium level, try adding a flocculant from the pool supply store. Another option is to drain some of the water and replace it.

Summary:
Purchase a water testing kit. Submerge the test strips for 15 seconds. Compare the results to the color chart. Look for a pH level between 7.2 and 7.8. Test for a chlorine level between 1 and 3 ppm. Aim for an alkalinity result between 120 and 150 ppm. Check that the cyanuric acid levels are between 20 and 30 ppm. Choose a calcium hardness level based on your pool type.