Plant nutrients used in hydroponics are dissolved in the water and are mostly in inorganic and ionic form.
Primary among the dissolved cations (positively charged ions) are
Ca2+ (calcium),
Mg2+ (magnesium), and
K+ (potassium);
the major nutrient anions in nutrient solutions are
NO−
3 (nitrate),
SO2−
4 (sulfate), and
H
2PO−
4 (dihydrogen phosphate).
Numerous 'recipes' for hydroponic solutions are available. Many use different combinations of chemicals to reach similar total final compositions. Commonly used chemicals for the macro nutrients include potassium nitrate, Potassium sulfate, ammonium sulfate , Di ammonium Phosphate calcium nitrate, Calcium sulphate, potassium phosphate, and magnesium sulfate. Various micro nutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe (iron), Mn (manganese), Cu (copper), Zn (zinc), B (boron), Cl (chlorine), and Ni (nickel).
Chelating agents are sometimes used to keep Fe soluble, and humic acids can be added to increase nutrient uptake.
Plants will change the composition of the nutrient solutions upon contact by depleting specific nutrients more rapidly than others, removing water from the solution, and altering the pH by excretion of either acidity or alkalinity. Care is required not to allow salt concentrations to become too high, nutrients to become too depleted, or pH to wander far from the desired value. The well-oxygenated and enlightened environment promotes the development of algae. It is therefore necessary to wrap the tank with black film obscuring all light.
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