Greenhouse Acid Injection Calculator
Enter the source-water alkalinity, target alkalinity, acid concentration, and injector setup. The calculator gives the dose per 100 gallons, the direct batch dose, the stock-tank recipe, and the nutrient added by the acid.
Acid per 100 gallons (93% sulfuric acid)23 mL (0.78 fl oz)
- Alkalinity to neutralize (mg/L as CaCO3)
- 100
- Acid for the water batch
- 230 mL (7.78 fl oz)
- Water treated per stock tank
- 1,000
- Acid to add to the stock tank
- 230 mL (7.78 fl oz)
- Acid concentration in stock solution
- 0.61%
- Nutrient contribution
- 33.91 ppm sulfate-equivalent
This estimates alkalinity neutralization, not final pH; confirm the dose with a small pilot batch and calibrated measurements.
Always add acid to water, use acid-compatible equipment, and follow the product safety data sheet.
Use the measured injector ratio when possible because nominal 1:X settings can drift.
The selected acid adds about 33.91 ppm sulfate-equivalent; compare that with the fertility program.
How to use this calculator
- Enter the measured alkalinity of the water in mg/L as CaCO3, not the water pH.
- Enter the residual alkalinity target for the crop, substrate, and container size.
- Choose the exact acid concentration shown on the product label.
- Enter either the batch volume to treat directly or the injector ratio and final stock-tank volume.
- Review the stock concentration, nutrient contribution, and safety notes before mixing.
How the acid dose is calculated
This calculator follows the greenhouse acidification procedure commonly taught by extension services: reduce alkalinity by a target amount, then multiply that reduction by an acid-specific factor. Alkalinity is entered as mg/L as CaCO3 because alkalinity is the water's acid-neutralizing capacity. Water pH alone does not tell you how much acid is needed.
Let A0 be current alkalinity and At be target alkalinity. The alkalinity to neutralize is:
D = max(A0 - At, 0)
The acid dose for 100 U.S. gallons is:
acid mL per 100 gal = D x F
- F = 0.23 for 93% sulfuric acid.
- F = 0.56 for 63% nitric acid.
- F = 0.70 for 75% phosphoric acid.
The direct batch dose scales from the 100-gallon result: batch acid = acid per 100 gal x batch gallons / 100. For an injector, the stock tank must contain enough acid for all water treated by that tank. The calculator uses treated gallons = injector ratio x stock gallons, then applies the same 100-gallon dose to that treated volume.
Stock solution and nutrient checks
The stock concentration is the acid volume divided by the final stock-tank volume. If the required acid equals or exceeds the final tank volume, the calculator rejects the setup because there is no usable dilution water in the stock tank. Concentrated stock results also receive a caution to check heat release, chemical compatibility, and injector materials before mixing.
Each acid adds a plant nutrient. The calculator multiplies the fluid ounces of acid per 100 gallons by the published coefficient for the selected acid: sulfate-equivalent for sulfuric acid, nitrate-equivalent for nitric acid, or phosphate-equivalent for phosphoric acid. This is shown so the acid choice can be compared with the fertilizer program instead of treated as neutral chemistry.
What moves the result most
The alkalinity reduction drives the dose directly. Reducing alkalinity by 100 mg/L as CaCO3 needs twice as much acid as reducing it by 50 mg/L. Acid choice also matters: at the listed concentrations, phosphoric acid needs more milliliters than sulfuric acid for the same alkalinity reduction, and it adds phosphate that may already be supplied by fertilizer.
What this calculator leaves out
The result estimates alkalinity neutralization, not a guaranteed final pH. Starting pH, bicarbonate and carbonate balance, water temperature, fertilizer reactions, substrate lime, crop uptake, injector calibration, and acid product differences can all change the observed pH. Use the number as a starting dose, then verify it with a small pilot batch and calibrated alkalinity and pH measurements before treating crop water at scale.
Worked example
Suppose a greenhouse has 250 mg/L alkalinity as CaCO3 and wants 150 mg/L after treatment. The reduction is 250 - 150 = 100 mg/L. With 93% sulfuric acid, the 100-gallon dose is 100 x 0.23, or 23.00 mL. That is 0.78 fluid ounces per 100 gallons.
For a 1,000-gallon reservoir, the direct batch dose is 230.00 mL, or 7.78 fluid ounces. A 10-gallon stock tank feeding a 1:100 injector treats 1,000 gallons, so that stock tank also needs 230.00 mL, or 7.78 fluid ounces, of acid. The stock solution is 0.61% acid by volume, and the sulfuric acid adds about 33.91 ppm sulfate-equivalent.
Common questions
What is the difference between water pH and alkalinity?
Water pH tells you how acidic or basic the water is at the moment of measurement. Alkalinity tells you how much acid the water can neutralize, which is why acid dosing is based on alkalinity rather than pH alone. Two water samples with the same pH can require very different acid amounts.
What target alkalinity should a greenhouse use?
The right target depends on crop sensitivity, substrate lime, container size, fertilizer acidity, and irrigation frequency. Many greenhouse programs aim for a moderate residual alkalinity rather than zero so pH does not swing too sharply. Use local extension guidance and crop records to set the target.
How much sulfuric acid lowers alkalinity?
For 93% sulfuric acid, the factor used here is 0.23 mL per ppm alkalinity removed per 100 U.S. gallons. Lowering alkalinity by 100 mg/L as CaCO3 therefore takes 23 mL, or about 0.78 fluid ounces, per 100 gallons. The product concentration must match the listed 93% strength.
How do I mix acid for a 1:100 injector?
First calculate the acid needed per 100 gallons of finished irrigation water. A stock tank on a 1:100 injector treats about 100 times its final stock volume, so a 10-gallon stock tank treats about 1,000 gallons. Add the calculated acid to water in the stock tank, then bring the tank to its final marked volume.
Should acid be added before or after fertilizer?
Acid is often injected ahead of fertilizer so alkalinity is reduced before nutrients reach the crop, but compatibility and injector layout matter. Some fertilizers and acids can react or precipitate when concentrated together. Keep incompatible materials in separate stock tanks and follow the fertilizer label, acid safety data sheet, and injector manufacturer guidance.
Why should the calculated dose be verified with a pilot test?
Published factors are good starting points, but real water chemistry and product strength can vary. A pilot batch confirms that the treated water reaches the intended alkalinity and pH before a large reservoir or irrigation line is dosed. Recheck when the water source, acid drum, fertilizer program, or injector calibration changes.