Fertilizer solubility is one of the key elements in making hydroponic nutrient stock solutions.  If you know the fertilizer solubility, you can make optimum stock solutions for any size nutrient tank.

Making stock solutions is extremely simple. All you have to do is to calculate the amount of fertilizers required to make a normal 1:1 solution that can be used directly to irrigate plants. Multiply each amount by 100 and add that amount to the same size tank that would have been used for the 1:1 solution. The new solution is a 1:100 stock solution. If each amount of fertilizer has been multiplied by 50, it is a 1:50 solution. For example, if complex fertilizers are used and the recommended rate is 1 kg.1000 L-1 of chemical X and 1 kg.1000 L-1 of calcium nitrate, a 1:100 stock solution would require 100 kg.1000 L-1 of chemical X and 100 kg.1000 L-1 of calcium nitrate. It is important that the size of the tank is not changed.

An important aspect to take into consideration is the fertilizer solubility.  The fertilizer solubility value is the saturation point to which each fertilizer can be dissolved before the various components precipitate   The fertilizer solubility value is not a fixed value, it varies according to temperature of the water.  Increasing the water temperature will increase the fertilizer solubility value.  This is important because mixing close to the maximum solubility limit in hot weather, can cause precipitation during the night when water temperature drops.

If you accidentally mixed too much fertilizer and a precipitate forms, just add more water to the tank.  It will take some time for the precipitate to dissolve again.

Common fertilizer solvability ratios in 25°C water are:

Approximate solubility levels (g.100ml-1) in cold water (25 °C) of some common used fertilizers used in hydroponics.
FertilizerChemical formulationSolubility
Ammonium nitrateNH4NO31180
Ammonium sulphate(NH4)2SO4706
Di-ammonium phosphate(NH4)2HPO4575
Potassium dihydrogen orthophosphateKH2PO4330
Potassium nitrateKNO3133
Potassium sulphateK2PO4120
Calcium nitrateCa(NO3)2.4H2O1212
Calcium sulphateCaSO40.209
Iron sulphateFeSO4.7H2O157
Magnesium sulphateMgSO4.7H2O 710
Magnesium nitrateMg(NO3)2.4 H2O4264
Manganese sulphateMnSO4.4H2O1053
Boric acidH3BO3 60
Copper sulphateCuSO4.5H2O316
Ammonium molybdate(NH4)6Mo7O244H2O 430
Zinc sulphateZnSO4.7H2O960
Phosphoric acidH3PO4 5480