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 |
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.