Get a bulk amount of hydroponic three part fertilizer, includes enough fertilizer to make 200 gallons.
This is similar to MasterBlend, which is $25 for 2.5 pounds on amazon.
Be wary of any dry two part fertilizer, Calcium Nitrate and Magnesium Sulfate should not by dry mixed into the same package. On improper mixing it will form calcium sulfate dihydrate (Gypsum), two part solutions are even harder to properly mix to avoid this reaction. Gypsum is denser than water, and will rob your plant of needed nutrients.