- Quote the manufacturer’s 3.6 / 1.1 / 2.4 g per US gallon example and explain the dissolving order behind it.
- Trace each gram figure through the assumed analyses to elemental ppm, and switch the batch to litres.
- Separate what the readout calculates from what it leaves out: source water, strength, sulfur, micronutrients and pH.
Recipe and elemental ppm calculator
24 g 4-18-38 + 15 g magnesium sulfate + 24 g calcium nitrate per 40 L final solution. Calcium nitrate analysis assumed 15.5% N / 19% Ca; magnesium sulfate assumed 9.86% Mg. Check the actual bags.
Manufacturer’s published mixing example ↗
Check or edit fertilizer label assumptions
Use percent by mass. P and K label fields are P₂O₅ and K₂O. Changing these affects elemental totals, while the recipe’s product weights stay fixed. Blank or invalid analysis produces no result.
Add measured source-water elemental concentrations
Default zero is an assumption of no contribution. Enter laboratory elemental mg/L, never hardness as CaCO₃ or nitrate reported as NO₃ without conversion.
24 g Masterblend 4-18-38, 15 g Magnesium sulfate heptahydrate, 24 g Calcium nitrate; totals N 117, P 47.13, K 189.26, Ca 114, Mg 39.98 mg/L
| Element | Fertilizer added | Source water | Total |
|---|---|---|---|
| N | 117 | 0 | 117 |
| P | 47.13 | 0 | 47.13 |
| K | 189.26 | 0 | 189.26 |
| Ca | 114 | 0 | 114 |
| Mg | 39.98 | 0 | 39.98 |
Five-element accounting only. No prediction of EC, uptake, precipitation or crop suitability. Sulfur and micronutrients are outside this readout. Do not use these mineral-feed recipes in a coupled fish system.
01 / What the manufacturer actually publishes
Jack’s Nutrients’ mixing article gives one rate for its 321 program, per US gallon of finished solution: “3.6 grams/gallon Part A (5-12-26) and dissolve then add 1.1 grams/gallon Epsom Salts and dissolve completely then add 2.4 grams/gallon Part B (Calcium Nitrate)”. That is the whole published recipe: it names only controlled-environment crops in general, gives no growth stage, EC or pH, and for anything beyond the single rate points readers to the company’s grow schedules page.
The name is a ratio label, not a weighing instruction; the nutrient mixing chapter covers why 3-2-1 is not 3 g, 2 g and 1 g, and that a US gallon is 3.785 L. This site treats the recipe as a manufacturer’s worked example when discussing leafy and fruiting food crops; the article publishes no food-crop rate, and nothing here is a target for your crop.
Reading: How do I mix Jack’s 321? ↗
02 / Why A and B are dissolved separately
The published order (A, then Epsom salt, then B, each dissolved before the next) has a reason. University of Missouri Extension G6984 explains that hydroponic recipes commonly use one formulation that provides calcium (15-0-0) and another that provides the rest of the nutrients (5-12-26), and that “Calcium from one formulation will immediately react with phosphorus and sulfate from the other formulation, creating insoluble particles that will sink to the bottom of the tank making them unavailable for plant roots.” G6984’s remedy is to dissolve each formulation separately, and its Figure 3 caption extends the same separation to concentrated fertilizer solutions fed through separate injectors.
At working strength each product goes into the full volume of moving water and dissolves before the next is added; dilution keeps calcium, phosphate and sulfate apart. Never dissolve A and B together as a shared concentrate or hold them in one stock tank; the stock solutions chapter covers separate A and B tanks.
Reading: Hydroponic Nutrient Solutions (G6984) ↗ · How do I mix Jack’s 321? ↗
03 / The analysis the calculator assumes
Grams become ppm only through a label analysis, and the calculator on this page uses explicit, editable assumptions: Part A is 5-12-26 with 6.3% Mg, Part B is 15% N with 18% Ca, and Epsom salt (magnesium sulfate heptahydrate) is 9.86% Mg. Phosphate and potash become elements through P₂O₅ × 0.4364 and K₂O × 0.8301, and each gram figure is divided by 3.785 L, so 3.6 g Part A is 0.951 g/L.
Under those assumptions the site’s arithmetic tests verify the per-US-gallon result at N 142.7, P 49.8, K 205.3, Ca 114.1 and Mg 88.6 mg/L before any source-water contribution. Part A supplies all the P and K, a third of the N and two thirds of the Mg; Part B the rest of the N and all the Ca; Epsom salt only Mg, plus unreported sulfate. If your calcium nitrate bag reads 15.5% N and 19% Ca, Ca moves to 120.5 mg/L and N to 145.8; edit the assumption rather than accept the default.
| Product | g per US gal | Assumed analysis | N mg/L | P mg/L | K mg/L | Ca mg/L | Mg mg/L |
|---|---|---|---|---|---|---|---|
| Part A | 3.6 | 5-12-26, 6.3% Mg | 47.6 | 49.8 | 205.3 | 0 | 59.9 |
| Epsom salt | 1.1 | 9.86% Mg | 0 | 0 | 0 | 0 | 28.7 |
| Part B | 2.4 | 15% N, 18% Ca | 95.1 | 0 | 0 | 114.1 | 0 |
| Total | 7.1 | — | 142.7 | 49.8 | 205.3 | 114.1 | 88.6 |
Reading: How do I mix Jack’s 321? ↗ · Hydroponic Nutrient Solutions (G6984) ↗
04 / Litres and the bag in front of you
The calculator stores the recipe as grams per litre, so a batch in litres needs no conversion by you: enter the finished volume and it multiplies the unrounded g/L figures (0.951, 0.2906 and 0.634) by that number. For 20 L at full strength that is 19.02 g Part A, 5.81 g Epsom salt and 12.68 g Part B. The ppm columns do not move with volume; only the grams do.
Read your own bag before trusting the defaults. Product versions differ; section 03 shows what one Part B change does to the table. G6984 states that “Fertilizers marketed as a single bag formulation will not provide essential nutrients at the optimum levels” and describes the alternative as bundles sold as Part A and Part B; the fertilizer labels chapter explains which label lines feed the percentage fields.
Reading: Hydroponic Nutrient Solutions (G6984) ↗ · How do I mix Jack’s 321? ↗
05 / Strength, source water and what the readout leaves out
The manufacturer publishes one rate and no seedling, leafy or fruiting percentage, and this site does not invent one. The strength field scales every fertilizer contribution proportionally: 50% halves the grams and the fertilizer-added ppm, nothing else. Source water sits on top: Penn State’s irrigation-water guide states that calcium below 40 mg/L in water “will typically need fertilizer additions of calcium” while calcium above 100 mg/L “may lead to antagonism”, and that magnesium generally only causes problems below 25 mg/L. Enter the laboratory’s elemental Ca and Mg in the source-water fields, never hardness as CaCO₃.
The readout is five elements from three products; it does not calculate sulfur, micronutrients, pH, alkalinity, uptake or precipitation. G6984 adds that EC “does not confirm that each nutrient is at the target concentration” and that the only way to know your water is suitable is to test it for pH, EC, alkalinity and individual elements. The pH-adjustment chapter covers the mixed solution’s pH.
- Fill the reservoir with most of the final volume; record source-water EC, pH and any laboratory Ca and Mg.
- Add 3.6 g Part A per US gallon (0.951 g/L) to moving water; wait until no residue remains.
- Add 1.1 g Epsom salt per US gallon (0.291 g/L); dissolve completely.
- Add 2.4 g Part B per US gallon (0.634 g/L) last. Never combine A and B before dilution.
- Top up to the final volume mark, then measure and log EC and pH; the readout gives elemental ppm, not an EC or pH to compare against.
- Log grams, lot numbers, each bag’s printed analysis and the readings.
FIELD QUESTIONYou mix 20 L at 100% strength from bags labelled A 5-12-26 (6.3% Mg), Epsom salt 9.86% Mg and B 15-0-0 (18% Ca), in water a laboratory reports at 30 mg/L Ca and 10 mg/L Mg. What do you weigh, and what Ca and Mg does the calculator report?
Grams: 0.951 × 20 = 19.02 g A; 1.1 ÷ 3.785 × 20 = 5.81 g Epsom salt; 0.634 × 20 = 12.68 g B. Fertilizer-added Ca stays 114.1 mg/L and Mg 88.6 mg/L, because ppm does not depend on volume. With source water: Ca 144.1 mg/L; Mg 98.6 mg/L. Penn State’s 100 mg/L Ca remark describes raw water, not a mixed solution.
Reading: How do I mix Jack’s 321? ↗ · Interpreting Irrigation Water Tests ↗ · Hydroponic Nutrient Solutions (G6984) ↗
Parts & buying criteria
Build your own parts & cost worksheet →
Showing drip / dutch buckets. Quantities describe the teaching model. Specify real working volume, support, fittings and instruments for your installation.
01Nutrient reservoir1 · illustrated quantity+
Stores the measured nutrient solution beneath or beside the growing area.
Inspect: Compare the surface with the pump intake or lower roots; freeboard is deliberate.
Maintain: Record level before refilling, keep light out and verify temperature, EC and pH.
Opaque, cleanable, intended-use container with volume marks and service access.
Check size, materials and operating conditions with your chosen supplier before ordering.02Pump & supply1 · illustrated quantity+
Moves nutrient solution from the reservoir to the growing area.
Inspect: Trace installed lift and branching; the pump label does not prove delivered flow.
Maintain: Measure output after service and inspect intake, filter and minimum water level.
Pump curve matched to installed head, required pressure and service needs.
Check size, materials and operating conditions with your chosen supplier before ordering.03Dutch buckets3 illustrated · illustrated quantity+
Contain a large root-zone medium with a defined drainage outlet.
Inspect: Inspect the outlet height, any internal water reserve and the drain screen on each bucket.
Maintain: Verify each bucket drains freely after an event and inspect moisture at several depths in representative buckets.
Rigid, opaque, food-safe buckets with screened outlets on a supported gravity return.
Check size, materials and operating conditions with your chosen supplier before ordering.04Root-zone mediumFor illustrated containers · illustrated quantity+
Stores moisture and air around the roots in the illustrated containers.
Inspect: Compare the medium surface with irrigation and drainage.
Maintain: Inspect wetting at several depths; prevent fines from reaching drains and emitters.
Prepared, stable grade matched to the irrigation method and crop.
Check size, materials and operating conditions with your chosen supplier before ordering.05Drip emitters3 illustrated · illustrated quantity+
Distribute solution separately to each container.
Inspect: Trace the manifold and the small outlet above each plant position.
Maintain: Collect equal-time samples and compare output; flush the main line before installing emitters.
Emitter pressure requirements matched to pump and filter; flushable connections.
Check size, materials and operating conditions with your chosen supplier before ordering.06Gravity return1 · illustrated quantity+
Collects each bucket outlet into a supported return line to the reservoir.
Inspect: Follow each bucket outlet into the shared return and check the continuous fall to the reservoir.
Maintain: Test pump-off drain-back and keep roots and medium out of the outlet.
Accessible fittings and verified capacity under normal and fault conditions.
Check size, materials and operating conditions with your chosen supplier before ordering.Evidence beside the lesson.
Source checks: September 2026. The geometry, inspection exercises and worksheets are original teaching material. The named organizations have not endorsed or reviewed this site.
Published recipe rates and planning ranges retain their source context. Calculator equations are accounting tools; they do not predict uptake, yield, toxicity or safe stocking. Model dimensions, water speeds, roots and fish counts are illustrative. Verify species, crop, source water and product labels for a real system.
- Jack’s Nutrients · manufacturerHow do I mix Jack’s 321? ↗
Published 3.6 / 1.1 / 2.4 gram per US gallon mixing example.
- University of Missouri ExtensionHydroponic Nutrient Solutions (G6984) ↗
Solution preparation, elemental nutrition and measurement.
- Penn State ExtensionInterpreting Irrigation Water Tests ↗
Distinguishing alkalinity, pH, salts and source-water problems.
The next useful connections.
Nutrient mixing: from grams to elemental ppm
Scale two documented fertilizer examples, read the bag analysis and calculate what actually enters the final solution.
Interactive tool · 6 min + guided practice →Nutrients & mixingStock solutions and injectors
Calculate a dilution factor, keep incompatible salts apart and verify what the injector delivers.
6 min + guided practice →Nutrients & mixingMasterblend 4-18-38: the three-part recipe and its elemental ppm
Three bags against one published row: what each part adds, why calcium nitrate goes in last and alone.
Interactive tool · 7 min + guided practice →Nutrients & mixingReading fertilizer labels: N-P-K, the analysis panel and nitrogen form
A soluble fertilizer label states nitrogen, phosphate and potash by mass, then an analysis panel and a derived-from list; read all three before a gram goes into a recirculating tank.
Interactive tool · 7 min + guided practice →Nutrients & mixingAdjusting pH in hydroponics: acids, bases and alkalinity
The pH reading tells you which way to push a solution; the water’s alkalinity tells you how hard, and most adjusters leave a nutrient behind.
6 min + guided practice →