This is a pH up and down in a concentrated form.

Nutrifield pH up and pH down are tank controllers that will adjust your hydroponic solution to the desired pH.

pH is a measure of the acidity or alkalinity of a solution and the scale ranges from 1 to 14. A pH of 7.0 is considered neutral and is based on pure water. Solutions with a pH less than 7 are considered acidic, while those above 7 are considered basic (alkaline). pH effects nutrient uptake for most plants. The optimum pH range for plants is from 5.8 to 6.5.