The chemical elements consumed in the greatest quantities by plants are carbon, hydrogen, and oxygen. These are present in the environment in the form of water and carbon dioxide; energy is provided by sunlight. Nitrogen, phosphorus, potassium, and sulfur are also needed in relatively large quantities. Together, these are the elemental macronutrients for plants. Nutrients are labeled with an NPK ratio, this ratio represents the amounts of nitrogen, pottasium, and phophorus. Fertilizers with a high N ratio promote vegative growth while fertilizers with a high P and K ratio are for flowering.

A PPM meter measures the amount of dissolved solids in your nutrient solution. Purchasing a PPM meter is one of the best investments a serious gardener can make. Without a PPM meter measuring more than 1 gallon of nutrient solution becomes a hassle. By using a PPM meter you are taking all the guess work and tidious measuring out of the nutrient mixing process, by measuring the overall strength of the solution. Remember to always take a base reading of the water before mixing nutrients in, all sources of water except R/O water will have some dissolved solids to start with.