The fertilizer calculator uses the mixing instructions provided by the MHPGardener Youtube channel for both Tomatoes and Lettuce. It uses Masterblend 4-18-38 Tomato fertilizer as its base, and also requires Calcium Nitrate, Magnesium Sulfate (aka Epsom Salt), and water. Changing the quantities allows the same four ingredients to make nutrient solutions for both Tomatoes, and Lettuce, as well as other plants. You can use the nutrient solution provided by the calculator to grow vegetables using the Kratky Method, or any other type of hydroponic growing method.