A hydroponic nutrient calculator turns a target concentration (ppm) into grams of fertilizer per gallon, or the reverse. The core formula is short: grams per US gallon = target ppm × 3.785 ÷ (nutrient % × 10) . For example, 150 ppm nitrogen from calcium nitrate at 15.5% N needs about 3.7 g per gallon. Free tools like HydroBuddy do the same math for whole recipes, but an EC meter still has the final word.
Jacks 321 (the maker spells it Jack’s 321) is a two-part hydroponic nutrient program from JR Peters: 3.6 grams of Part A (5-12-26), 2.4 grams of Part B (calcium nitrate) and 1.1 grams of Epsom salt per US gallon of water. Mix in this order: dissolve Part A completely, then the Epsom salt, then Part B. Never combine the dry powders.
Yes, you can use hydroponic nutrients in soil . They’re complete, water-soluble fertilizers, and plants take up the same mineral ions either way. The catch is that soil and potting mix already hold nutrients and trap salts, so full hydroponic strength fed every watering can cause salt buildup and tip burn. Follow any soil directions on the label, feed once or twice a week with plain water between, and leach pots every two to three months.
The MaxiGro feeding schedule on the General Hydroponics label is simple: 1–2 teaspoons per gallon of fresh water (5–10 grams per 4 liters). In hydroponics, change the reservoir weekly. In soil, feed once or twice a week with plain water in between. Use mild strength for delicate plants and full strength for robust ones, then switch to MaxiBloom when plants begin flowering or setting fruit.
Fluoride in water for plants is harmless for most crops, but a short list of sensitive plants can develop brown leaf tips and scorched margins from fluoridated tap water. Dracaena (corn plant), spider plant, Tahitian bridal veil, yucca, lilies, tulips and gladiolus are the classic victims. If you grow them, water with rainwater, distilled or reverse osmosis (RO) water, skip perlite and superphosphate, and keep the root zone pH from running low.
The best hydroponic nutrients are complete, water-soluble formulas made for soilless growing, meaning they supply calcium, magnesium and chelated micronutrients, not just N-P-K. For most US home growers, General Hydroponics Flora Series is the most flexible pick, Masterblend 4-18-38 with calcium nitrate and Epsom salt is the budget pick, and the FoxFarm hydro trio suits growers who want a brand schedule.
Miracle Gro hydroponics is possible in a pinch, but it isn’t a good long-term plan. Miracle-Gro Water Soluble All Purpose Plant Food (24-8-16) supplies its nitrogen as ammonium and urea, lists no calcium or magnesium, and was made for soil. A complete hydroponic nutrient, or a 4-18-38 kit with calcium nitrate and Epsom salt, grows healthier plants for about the same effort.
The Masterblend 4-18-38 hydroponic recipe is 2.4 grams of Masterblend, 1.5 grams of magnesium sulfate (Epsom salt) and 2.4 grams of calcium nitrate per gallon of water. Dissolve the 4-18-38 first, then the Epsom salt, then the calcium nitrate last. Masterblend says to use half rates for seedlings until they are well established.
The Fox Farm hydroponic feeding schedule uses three base nutrients: Grow Big Hydroponic for vegetative growth, then Tiger Bloom plus Big Bloom once flowers appear, usually around week 5. FoxFarm’s labels call for about 2 teaspoons (10 mL) per gallon of Grow Big Hydro or Tiger Bloom per reservoir change, pH 5.8 to 6.3, and feeding by EC, not by the bottle alone.
The Flora Series feeding chart from General Hydroponics tells you how many milliliters of FloraMicro, FloraGro and FloraBloom to add per gallon at each growth stage. Seedlings start near 1.8 mL/gal of each part. Vegetative feeds lean on Micro and Gro, and bloom feeds lean on Bloom. Always add Micro to the water first, then Gro, then Bloom, and check EC and pH last.