This Ph kit is designed to work superbly in hydroponic environments, both soil-less mixtures and soil grown plants. Includes 8oz bottle of pH Up which is used to elevate it to the desired level. Contains 8oz bottle of pH down which uses food grade phosphoric acid to lower the pH to to the desired level. Includes pH Test Indicator tube:fill a test-tube halfway with nutrient, add a few drops of pH Test Indicator, and observe the coloration of the liquid in the vial. For best results, discard and replace hydroponic solution regularly. pH controls is essential for stimulating vigorous plant growth. The pH scale measures acidity or alkalinity on a scale of 0-14. This is model GH1514. Below 7.0 the pH is acidic. Above 7.0 , the pH is alkaline. 7.0 is nuetral. The best pH for general plant growth is in the range of 5.5 to 6.5, slightly acidic.Nutrient solution that is too high (basic) or too low (acidic) cannot be properly asbsorbed by plants. Incorrect nutrient solution pH can cause slow growth,sickly plants and low yields.