H test paper can only test the pH of water. When you buy it back, you will get a PH colorimetric card. Tear it off and immerse it in the liquid to be tested for 2-3 seconds, then take it out. Compared with the color chart, which color is close is a rough comparison. This is just a rough test. The concentration of hydrogen ions in the solution increases by 1 0 times with the decrease of pH value. But it actually reduces 1.