---
title: "Hydroponic Nutrient Dosing Calculator: Precise A/B Ratios and the Gypsum Lockout Risk Most Growers Miss"
canonical: "https://theyieldgrid.com/hydroponic-nutrient-dosing-calculator/"
model_id: "tyg-755"
model_version: "1.0.0"
last_reviewed: "2026-04-27T19:28:51"
reviewed_by: "Umer Hayiat"
---

# Hydroponic Nutrient Dosing Calculator: Precise A/B Ratios and the Gypsum Lockout Risk Most Growers Miss

> Canonical calculator: [https://theyieldgrid.com/hydroponic-nutrient-dosing-calculator/](https://theyieldgrid.com/hydroponic-nutrient-dosing-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - Hydroponic Nutrient Dosing Calculator: Precise A/B Ratios and the Gypsum Lockout Risk Most Growers Miss The math behind raising reservoir EC is straightforward multiplication. The part that trips up experienced growers and automated systems alike is the order and physical separation of Part A and Part B additions. Calcium Nitrate and Magnesium Sulfate cannot contact each other in concentrated form without reacting to form Calcium Sulfate, an insoluble precipitate that locks nutrients out of solution before plants ever see them. This page treats that chemistry as an engineering constraint, not a footnote.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Target Reservoir EC | `hydrndsizer_target_ec` | number | 0.1 – 5.0 mS/cm | 0.1 to 5.0 | No |
| Current Reservoir EC | `hydrndsizer_current_ec` | number | 0 – 5.0 mS/cm | 0 to 5.0 | No |
| Reservoir Volume | `hydrndsizer_volume` | number | 0.5 – 5,000 gallons | 0.5 to 5000 | No |
| Nutrient Concentration Factor | `hydrndsizer_factor` | number | gallon | 0.1 to 100 | No |

## Outputs

| Output ID | Default state |
|---|---|
| `hydrndsizer_target_ec_err` |  |
| `hydrndsizer_current_ec_err` |  |
| `hydrndsizer_volume_err` |  |
| `hydrndsizer_factor_err` |  |
| `hydrndsizer_results` | Dosing Results CALCIUM SULFATE PRECIPITATION RISK DETECTED Total Nutrient Dose — mL total (A + B combined) EC Deficit to Close — mS/cm needed Add Part A first — wait 5 minutes — then add Part B Part A (Calcium Nitrate) — Part B (Magnesium Sulfate) — EC Range: 0 → 5.0 mS/cm 0 1.0 2.0 3.0 4.0 5.0 Target EC (mS/cm) ΔEC (from current) Dose Per Part (mL) Total Dose (mL) Status |
| `hydrndsizer_precip_banner` | CALCIUM SULFATE PRECIPITATION RISK DETECTED |
| `hydrndsizer_out_primary` | — |
| `hydrndsizer_out_delta` | — |

## Formula and method

Visualizing the critical five-minute delay and physical separation required to keep Calcium and Sulfate ions from precipitating into solid gypsum. Show the calculation steps Step 1: Compute EC deficit (ΔEC) Subtract current reservoir EC from target EC. ΔEC = Target EC (mS/cm) – Current EC (mS/cm) If the result is zero or negative, no nutrients are needed. The tool returns a zero dose. Step 2: Compute total nutrient dose Multiply ΔEC by reservoir volume in gallons and by the concentration factor. Total Dose (mL) = ΔEC x Volume (gal) x Factor (mL/gal per 1.0 EC) This gives the combined volume of both nutrient parts required. Step 3: Split into Part A and Part B Standard 2-part A/B systems are dosed at a 1:1 ratio. Part A Dose (mL) = Total Dose / 2 Part B Dose (mL) = Total Dose / 2 Rounding is applied to one decimal place on the final result only, not to intermediate values. Step 4: Precipitation risk assessment If Part A dose per application is 1.0 mL or greater, the calculator flags a precipitation risk and displays the 5-minute addition protocol. At 50 mL or greater per part, the high-risk variant of the warning is shown, which includes specific guidance on injection point separation for automated dosers. Assumptions and Limits The EC response to nutrient addition is assumed to be linear. In practice, very high-EC solutions may exhibit slightly non-linear conductivity curves, particularly above 3.5 mS/cm. Water source EC is assumed to be reflected in the “Current Reservoir EC” input. If your source water contributes significant EC from calcium carbonate or other minerals, those ions occupy EC bandwidth without contributing the same nutrients as A/B formula ions. The concentration factor is assumed to be stable. Nutrient concentrate density can shift at extreme temperatures (below 10°C or above 35°C). Store stock solutions at room temperature before measuring. Part A and Part B are assumed to be added to a fully circulating reservoir. If circulation is off or flow is restricted, actual EC distribution will be uneven and your spot readings will be unreliable. The 1:1 Part A to Part B ratio applies to balanced 2-part systems. Some specialty formulas (bloom boosters, calcium-forward base nutrients) use non-equal ratios. Check your nutrient line’s protocol before applying split calculations from this tool. This tool does not model pH change from nutrient addition. Concentrated Calcium Nitrate additions can shift pH upward; Magnesium Sulfate additions are typically neutral to slightly acidic. Always check and adjust pH after dosing, after EC has stabilized. The calculator does not account for nutrient uptake between the time you take your current EC reading and the time you add nutrients. In high-transpiration conditions, EC can drop measurably within an hour.

## Verified worked examples

### Scenario 1: Small Home DWC System, Leafy Greens

Target EC: 1.8 mS/cm Current EC: 0.5 mS/cm Reservoir Volume: 20 gallons Concentration Factor: 5.0 mL/gal per 1.0 EC Result: ΔEC = 1.3 mS/cm. Total dose = 1.3 x 20 x 5.0 = 130 mL. Part A = 65 mL. Part B = 65 mL. A 20-gallon system is small enough that 65 mL additions carry meaningful precipitation risk if both are poured near the same spot. Add Part A near the air stone or pump return, wait 5 minutes, then add Part B at the opposite end of the reservoir.

### Scenario 2: Commercial NFT Channel System, Fruiting Tomatoes

Target EC: 2.8 mS/cm Current EC: 1.2 mS/cm Reservoir Volume: 150 gallons Concentration Factor: 4.5 mL/gal per 1.0 EC Result: ΔEC = 1.6 mS/cm. Total dose = 1.6 x 150 x 4.5 = 1,080 mL. Part A = 540 mL. Part B = 540 mL. The ΔEC of 1.6 mS/cm crosses the large-jump threshold. For mature fruiting plants this can be tolerated in one session, but running the system for an additional 15 minutes of circulation before recirculating to plant channels is advisable. The 540 mL per part is a high-volume addition that demands physically separated injection points.

### Scenario 3: Greenhouse Reservoir Refill After Dilution Event, Mixed Crops

Target EC: 2.5 mS/cm Current EC: 0.6 mS/cm (heavy fresh-water top-off overnight) Reservoir Volume: 300 gallons Concentration Factor: 5.0 mL/gal per 1.0 EC Result: ΔEC = 1.9 mS/cm. Total dose = 1.9 x 300 x 5.0 = 2,850 mL. Part A = 1,425 mL. Part B = 1,425 mL. A 1.9 mS/cm jump over 300 gallons represents a substantial total salt load. This scenario warrants splitting into two dosing sessions: dose to an intermediate EC of 1.5 first, let the system stabilize for several hours, then dose the remainder to 2.5. This protects root zones from a rapid osmotic shift after a dilution event.

## Assumptions

Visualizing the critical five-minute delay and physical separation required to keep Calcium and Sulfate ions from precipitating into solid gypsum. Show the calculation steps Step 1: Compute EC deficit (ΔEC) Subtract current reservoir EC from target EC. ΔEC = Target EC (mS/cm) – Current EC (mS/cm) If the result is zero or negative, no nutrients are needed. The tool returns a zero dose. Step 2: Compute total nutrient dose Multiply ΔEC by reservoir volume in gallons and by the concentration factor. Total Dose (mL) = ΔEC x Volume (gal) x Factor (mL/gal per 1.0 EC) This gives the combined volume of both nutrient parts required. Step 3: Split into Part A and Part B Standard 2-part A/B systems are dosed at a 1:1 ratio. Part A Dose (mL) = Total Dose / 2 Part B Dose (mL) = Total Dose / 2 Rounding is applied to one decimal place on the final result only, not to intermediate values. Step 4: Precipitation risk assessment If Part A dose per application is 1.0 mL or greater, the calculator flags a precipitation risk and displays the 5-minute addition protocol. At 50 mL or greater per part, the high-risk variant of the warning is shown, which includes specific guidance on injection point separation for automated dosers. Assumptions and Limits The EC response to nutrient addition is assumed to be linear. In practice, very high-EC solutions may exhibit slightly non-linear conductivity curves, particularly above 3.5 mS/cm. Water source EC is assumed to be reflected in the “Current Reservoir EC” input. If your source water contributes significant EC from calcium carbonate or other minerals, those ions occupy EC bandwidth without contributing the same nutrients as A/B formula ions. The concentration factor is assumed to be stable. Nutrient concentrate density can shift at extreme temperatures (below 10°C or above 35°C). Store stock solutions at room temperature before measuring. Part A and Part B are assumed to be added to a fully circulating reservoir. If circulation is off or flow is restricted, actual EC distribution will be uneven and your spot readings will be unreliable. The 1:1 Part A to Part B ratio applies to balanced 2-part systems. Some specialty formulas (bloom boosters, calcium-forward base nutrients) use non-equal ratios. Check your nutrient line’s protocol before applying split calculations from this tool. This tool does not model pH change from nutrient addition. Concentrated Calcium Nitrate additions can shift pH upward; Magnesium Sulfate additions are typically neutral to slightly acidic. Always check and adjust pH after dosing, after EC has stabilized. The calculator does not account for nutrient uptake between the time you take your current EC reading and the time you add nutrients. In high-transpiration conditions, EC can drop measurably within an hour. The EC response to nutrient addition is assumed to be linear. In practice, very high-EC solutions may exhibit slightly non-linear conductivity curves, particularly above 3.5 mS/cm. Water source EC is assumed to be reflected in the “Current Reservoir EC” input. If your source water contributes significant EC from calcium carbonate or other minerals, those ions occupy EC bandwidth without contributing the same nutrients as A/B formula ions. The concentration factor is assumed to be stable. Nutrient concentrate density can shift at extreme temperatures (below 10°C or above 35°C). Store stock solutions at room temperature before measuring. Part A and Part B are assumed to be added to a fully circulating reservoir. If circulation is off or flow is restricted, actual EC distribution will be uneven and your spot readings will be unreliable. The 1:1 Part A to Part B ratio applies to balanced 2-part systems. Some specialty formulas (bloom boosters, calcium-forward base nutrients) use non-equal ratios. Check your nutrient line’s protocol before applying split calculations from this tool. This tool does not model pH change from nutrient addition. Concentrated Calcium Nitrate additions can shift pH upward; Magnesium Sulfate additions are typically neutral to slightly acidic. Always check and adjust pH after dosing, after EC has stabilized. The calculator does not account for nutrient uptake between the time you take your current EC reading and the time you add nutrients. In high-transpiration conditions, EC can drop measurably within an hour. The chemistry driving these warnings is not a preference or a manufacturer guideline. It is solubility physics. Critical Warnings Simultaneous injection creates Gypsum: When concentrated Calcium Nitrate (Part A) and Magnesium Sulfate (Part B) contact each other before dispersing, the reaction Ca2+ + SO42- produces Calcium Sulfate (CaSO4). This compound is sparingly soluble and precipitates immediately as a white powder. It settles to the reservoir floor and is biologically unavailable to plants. No amount of subsequent mixing recovers it. Your EC meter will read the correct target value while actual bioavailable calcium and sulfur are partially locked out in solid form. Automated dosers are the highest-risk setup: Peristaltic pump systems that inject Part A and Part B through tubes positioned close together in the reservoir are a common source of chronic, hard-to-diagnose calcium deficiency in otherwise well-managed systems. The precipitation happens at the injection zone before bulk water dilution occurs. Injection points should be separated by at least 12 inches, with the circulation pump positioned to rapidly sweep both injection zones. For automated systems, a minimum 5-minute timer delay between Part A and Part B dosing cycles is a baseline safety standard. Large EC jumps stress root zones: A single-session ΔEC above 1.5 mS/cm produces a rapid increase in osmotic potential in the root zone. For plants already under heat or transpiration stress, this can trigger wilting that resembles underwatering, even though the reservoir is full. Stage large doses across multiple sessions separated by at least several hours, with EC verification between each. EC-correct does not mean nutrient-complete: After a precipitation event, EC can read exactly at target because the remaining dissolved ions maintain conductivity, but the ionic ratios are shifted. Calcium and sulfur are under-represented. Deficiency symptoms (blossom end rot, tip burn in leafy crops) can emerge weeks after a single significant precipitation event. Minimum Operating Standards Always run your circulation pump before, during, and for at least 10 minutes after any nutrient addition. Circulation is not optional; it is what determines whether concentrated nutrients precipitate or disperse safely. Verify EC with a calibrated meter after every dosing session, taken 10 minutes after the final addition with full circulation running. Calibrate your EC meter against reference solution at least monthly. Never add nutrients to a stagnant reservoir. If your pump is off for any reason, restore circulation first and verify it is running before dosing. A properly sized air pump running continuously in deep water culture systems provides the baseline agitation that prevents localized concentration spikes at injection points. Competitor Trap: Most nutrient dosing guides online focus entirely on the dose volume calculation and treat A/B addition order as a casual tip in a sidebar. This framing is misleading because the precipitation risk is not merely a best-practice suggestion; it is a chemical constraint that operates independent of grower intent. A system where Part A and Part B are added without spatial separation or timing delays will produce gypsum precipitation on every dosing cycle. The deficiency symptoms that result, commonly misread as pH imbalance or magnesium shortage, lead growers to add more nutrients or adjust pH repeatedly without fixing the actual cause. The 5-minute delay and separated injection points are the only reliable mechanical controls against this failure mode. Managing nutrient solution chemistry involves more than EC alone. If you are running an NFT or recirculating system where channel flow rates influence nutrient delivery, cross-reference your system design with the NFT hydroponics calculator to confirm your flow rate supports the nutrient concentrations you are targeting.

## Limitations and safety

The EC response to nutrient addition is assumed to be linear. In practice, very high-EC solutions may exhibit slightly non-linear conductivity curves, particularly above 3.5 mS/cm. Water source EC is assumed to be reflected in the “Current Reservoir EC” input. If your source water contributes significant EC from calcium carbonate or other minerals, those ions occupy EC bandwidth without contributing the same nutrients as A/B formula ions. The concentration factor is assumed to be stable. Nutrient concentrate density can shift at extreme temperatures (below 10°C or above 35°C). Store stock solutions at room temperature before measuring. Part A and Part B are assumed to be added to a fully circulating reservoir. If circulation is off or flow is restricted, actual EC distribution will be uneven and your spot readings will be unreliable. The 1:1 Part A to Part B ratio applies to balanced 2-part systems. Some specialty formulas (bloom boosters, calcium-forward base nutrients) use non-equal ratios. Check your nutrient line’s protocol before applying split calculations from this tool. This tool does not model pH change from nutrient addition. Concentrated Calcium Nitrate additions can shift pH upward; Magnesium Sulfate additions are typically neutral to slightly acidic. Always check and adjust pH after dosing, after EC has stabilized. The calculator does not account for nutrient uptake between the time you take your current EC reading and the time you add nutrients. In high-transpiration conditions, EC can drop measurably within an hour. The chemistry driving these warnings is not a preference or a manufacturer guideline. It is solubility physics. Critical Warnings Simultaneous injection creates Gypsum: When concentrated Calcium Nitrate (Part A) and Magnesium Sulfate (Part B) contact each other before dispersing, the reaction Ca2+ + SO42- produces Calcium Sulfate (CaSO4). This compound is sparingly soluble and precipitates immediately as a white powder. It settles to the reservoir floor and is biologically unavailable to plants. No amount of subsequent mixing recovers it. Your EC meter will read the correct target value while actual bioavailable calcium and sulfur are partially locked out in solid form. Automated dosers are the highest-risk setup: Peristaltic pump systems that inject Part A and Part B through tubes positioned close together in the reservoir are a common source of chronic, hard-to-diagnose calcium deficiency in otherwise well-managed systems. The precipitation happens at the injection zone before bulk water dilution occurs. Injection points should be separated by at least 12 inches, with the circulation pump positioned to rapidly sweep both injection zones. For automated systems, a minimum 5-minute timer delay between Part A and Part B dosing cycles is a baseline safety standard. Large EC jumps stress root zones: A single-session ΔEC above 1.5 mS/cm produces a rapid increase in osmotic potential in the root zone. For plants already under heat or transpiration stress, this can trigger wilting that resembles underwatering, even though the reservoir is full. Stage large doses across multiple sessions separated by at least several hours, with EC verification between each. EC-correct does not mean nutrient-complete: After a precipitation event, EC can read exactly at target because the remaining dissolved ions maintain conductivity, but the ionic ratios are shifted. Calcium and sulfur are under-represented. Deficiency symptoms (blossom end rot, tip burn in leafy crops) can emerge weeks after a single significant precipitation event. Minimum Operating Standards Always run your circulation pump before, during, and for at least 10 minutes after any nutrient addition. Circulation is not optional; it is what determines whether concentrated nutrients precipitate or disperse safely. Verify EC with a calibrated meter after every dosing session, taken 10 minutes after the final addition with full circulation running. Calibrate your EC meter against reference solution at least monthly. Never add nutrients to a stagnant reservoir. If your pump is off for any reason, restore circulation first and verify it is running before dosing. A properly sized air pump running continuously in deep water culture systems provides the baseline agitation that prevents localized concentration spikes at injection points. Competitor Trap: Most nutrient dosing guides online focus entirely on the dose volume calculation and treat A/B addition order as a casual tip in a sidebar. This framing is misleading because the precipitation risk is not merely a best-practice suggestion; it is a chemical constraint that operates independent of grower intent. A system where Part A and Part B are added without spatial separation or timing delays will produce gypsum precipitation on every dosing cycle. The deficiency symptoms that result, commonly misread as pH imbalance or magnesium shortage, lead growers to add more nutrients or adjust pH repeatedly without fixing the actual cause. The 5-minute delay and separated injection points are the only reliable mechanical controls against this failure mode. Managing nutrient solution chemistry involves more than EC alone. If you are running an NFT or recirculating system where channel flow rates influence nutrient delivery, cross-reference your system design with the NFT hydroponics calculator to confirm your flow rate supports the nutrient concentrations you are targeting.

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## Provenance

- Model ID: `tyg-755`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-04-27T19:28:51
- Runtime SHA-256: `91541454372a262d148a76aca555b8cd8f9b3d795e23ccde025f096605ad00c8`

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