Flex Commercial Solutions pH Down lowers and maintains the pH levels for hydroponic systems, soil, and other grow media. Maintaining pH levels is especially important due to varying water quality, hard water can raise the pH levels which hinders a plant’s ability to uptake essential nutrients. It is recommended to check pH levels daily for optimal results. Ideal pH ranges are 5.5 to 5.8 for hydroponics and 6.2 to 6.3 for soils, potted plants, and sphagnum moss.