Hydroponics is chemistry as it is as much farming. Unlike soil that is forgiving and stable when it comes to pH, hydroponics is a different story. The pH of water in hydroponics can change overnight. Air, rain, medium, can all affect the pH of your water and when pH goes out of range, plants get injured or the very least, suffer from stunted growth.
One must understand that a crop thrives only at a given pH range. Lettuce for instance is known to grow best between 5.5 to 6.5 a range considered to be slightly acidic. Do note that a pH level between 6 and 7 is 1,000 more acidic than the other so do take pH very seriously. Beyond a crop’s prescribed range, nutrient deficiency occurs. Below the ph range and plants will suffer from micronutrient toxicity and macronutrient deficiency. While above the pH range, plants will suffer from micronutrient deficiency and over nutrient from macronutrients.
As they say, pH is the key.