Every plant needs certain levels of nutrients in order to thrive and grow to its maximum potential. The different stages of life of a plant require different nutrients that need to be added.
When working with hydroponics, nutrients are the life line of plants. With no other way of gaining the proper essential nutrition, nutrients need to be added into the water of hydroponic systems.
The science of nutrients is a complicated one. Too much, too little, wrong kind, wrong time, all of which can hurt or kill your plants.
What deficiency does your plant have?