pH adjusters allow gardeners to adjust the pH level of their plant’s nutrient solution. The fertilizer being fed to your plants should be slightly acidic in the range of 5.5 to 6.5. pH is the measurement of acid or base in something. The pH range is from 0-14, where 7 is neutral. Low numbers are acids and high numbers are bases. The higher or lower the number, the more extreme the acid or base becomes. Lemons have a very low pH where soap has a very high pH. Shifting pH levels allow for different elements to be taken up.