MasterBlend 4-18-38 Calculator
Enter your reservoir size and the strength you want. You get the grams of MasterBlend 4-18-38, calcium nitrate and Epsom salt to dissolve, using the common 2 : 2 : 1 ratio.
How the calculation works
All three ingredients scale with the volume of water and with the strength you choose. First the reservoir is converted to US gallons, then:
MasterBlend (g) = strength × gallons, Calcium nitrate (g) = MasterBlend × ratio, Epsom salt (g) = MasterBlend × ratio
Example: a 20 litre reservoir is 20 ÷ 3.785 = 5.28 gallons. At 2.4 g per gallon you need 2.4 × 5.28 = 12.7 g of MasterBlend, 12.7 g of calcium nitrate (ratio 1) and 6.3 g of Epsom salt (ratio 0.5).
The default of 2.4 g, 2.4 g and 1.2 g per gallon is a commonly shared recipe, not an official figure from the manufacturer. Use a lower strength for seedlings, and check the result with a meter using the EC to PPM converter.
Dissolve each ingredient separately in water and stir well. Weigh with a scale that reads to 0.1 g. Always follow the label of the product you buy.
Frequently asked questions
What is the usual MasterBlend, calcium nitrate and Epsom salt ratio?
A widely shared recipe is 2.4 g of MasterBlend 4-18-38, 2.4 g of calcium nitrate and 1.2 g of Epsom salt (magnesium sulphate) per US gallon of water, which is a 2 : 2 : 1 ratio by weight. Some growers use a little less for young plants and a little more for fruiting plants. Check your product's label for its own recommendation.
Why are three ingredients needed?
MasterBlend 4-18-38 supplies nitrogen, phosphorus, potassium and trace elements but no calcium or magnesium in useful amounts. Calcium nitrate adds calcium and more nitrogen, and Epsom salt adds magnesium. The three together make a complete mix.
Can I dissolve them all together?
Not in a concentrated stock. Calcium nitrate can react with the sulphates in the other two and form a solid. Dissolve each ingredient in the water separately and stir well between additions.
Is this the right tool for liquid nutrients?
No. This tool is for the powdered three-part recipe, measured in grams. For liquid bottle nutrients, use the hydroponic nutrient calculator.