Primary Hydroponic Nutrients
Nitrogen (N) is the most important nutrient for leaf and stem development. Most plants need more nitrogen during the vegetative growth phase. Hydroponic nutrient solutions with "grow" or "flower" in their name usually contain an extra boost of nitrogen for vegetating plants. Nitrogen deficiency is the most common plant problem found in hydroponic growing systems. Soft, weak plants and yellow leaves are signs of nitrogen deficiency.
When plants are in transition between growing phases, it may be better to use only a half-strength nitrogen mix in your solution. This will prevent your plant from stretching while it is switching its energy over to flower development. Resume feeding with your regular mix of hydroponic nutrients after the plant is fully into flowering stage.
Phosphorus (P) is crucial for root and flower development. Slow and/or stunted growth could be a sign of phosphorus deficiency. Phosphorus becomes even more important during the flowering stage. Most "Bloom" type formulas contain a breakdown of 0-50-30, which means they contain no nitrogen and much higher levels of phosphorus and potassium.
Potassium (K) is different from the other two hydroponic nutrients in that it doesn't feed the plant directly in any stage of growth. It regulates and aids the intake of the other primary and secondary nutrients. Without sufficient potassium, your plant may experience irregular growth and increased susceptibility to disease and pests. You should give less potassium during flowering because it inhibits fruit production.