A hydroponics system requires the right balance of nutrients for your plants to grow properly because there's no soil to help the process. Soil provides the necessary nutrients for plants, and if one of those elements is missing in your nutrient solution, you will have wilted, brown plants or plants that do not grow at all.
A plant that does not have enough nitrogen will grow yellow and pale, while plants with too much will have thick leaves and little fruit growth. Nitrogen comes in two forms: ammonia-based and nitrate-based, with most plants needing the former.
Plants that produce fruits or vegetables require a good amount of phosphorous to grow properly. Darkened leaves or vegetables that look purplish are likely to have a phosphorous deficiency. Phosphorous also helps the growth of plants' roots.
Potassium is required for the "fruiting" or blooming stage, when all of the energy the plant can muster goes into growing the fruit of vegetable of the plant. Potassium deficiencies usually show up as a wilting and loss of lower leaves on the plant, and a browning of other leaf edges.
Calcium is required for the growth of a proper and healthy root system. Calcium deficiencies will often cause the plant to turn brown and the leaves to wilt.
Magnesium and Sulphur
Magnesium is required for the photosynthetic process and needed in large amounts for a plant's survival. A lack of magnesium means a plant can not properly feed itself with light, and it will wilt and die quickly. Sulfur is usually associated with magnesium, as plants usually get their supply in the magnesium sulfate mixture. A lack of sulfur creates yellow leaves.
Plants also require in smaller amounts iron, boron, manganese, zinc, copper, molybdenum and chlorine. These nutrients are included in all hydroponic nutrient solutions you will buy. They keep the plant from looking undesirable and prevent brittle leaves, stems and ill-shaped fruit.
Combining the Nutrients
All of these nutrients combine to make a complete solution for your plants' needs. You can use commercial products, which can be found at a variety of online retailers or specialized garden centers, or you can make your own solutions by combining individual nutrients. Doing it yourself can be tricky; the wrong combination of nutrients can kill off your plant. Solutions can be made by combining individual nutrients in separate, concentrated formulas, then mixing them together in a tub of water. This method can be confusing--getting all of the individual nutrients can be time consuming, while getting the correct amounts can be downright frustrating. If you are a beginner, buy your hydroponic solution from a retailer and move on to homemade solutions once you have become more knowledgeable.