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A simple cheatsheet for macro nutrient additions in hydroponics

In hydroponic growing, we are often faced with the need to adjust the nutrient concentrations of a fertilizer reservoir or foliar spray directly, in order to increase the quantity of some nutrient by a specific amount. Although you can use a program like HydroBuddy in order to quickly calculate these values, it is often the case that these calculations need to be done in the field or in a growing environment, and a computer to calculate things is not at hand. For this reason, I have created a small “cheat sheet” that you can use in order to figure out the amounts of salts that you would need to add to a solution to increase any of the macronutrients by 10 ppm.

Salt Name ppm Element ppm  Element g/L g/gal
Calcium nitrate (ag grade) 10 N (NO3-) 13.19 Ca 0.0694 0.2629
MAP 10 N (NH4+) 22.1 P 0.0821 0.3108
Ammonium Sulfate 10 N (NH4+) 11.4 S 0.0472 0.1785
Gypsum 10 Ca 7.99 S 0.0430 0.1626
Calcium Chloride 10 Ca 17.69 Cl 0.0277 0.1048
Magnesium Nitrate Hexahydrate 10 N (NO3-) 8.67 Mg 0.0915 0.3463
Epsom Salt 10 Mg 13.19 S 0.1014 0.3839
Magnesium Chloride 10 Mg 29.16 Cl 0.0392 0.1483
AgSil 16H 10 Si 10.9 K 0.0411 0.1554
MKP 10 P 12.62 K 0.0439 0.1663
Potassium Nitrate 10 N (NO3-) 27.87 K 0.0730 0.2763
Potassium Sulfate 10 K 4.10 S 0.0223 0.0844
Potassium Chloride 10 K 9.067 Cl 0.0191 0.0722
Cheatsheet for macronutrient additions in hydroponics

With the above cheatsheet, you can quickly evaluate some of the most common options you would have to increase all the different macronutrients in a hydroponic or foliar solution by 10 ppm and which secondary elemental contributions you would get from these additions. For example, if you add 0.0694g/L of Calcium Nitrate, this would add 10ppm of Nitrogen as nitrate plus 13.19ppm of Calcium. Careful consideration of secondary contributions need to be taken into account, especially when using salts that contain elements that can be toxic, such as chlorides.