Using acids in Hydroponics, Irrigation & Fertigation

Water quality is one of the most important—and most overlooked—factors in hydroponics and fertigation.
Acids play a key role in:

• Reducing neutralizing alkalinity (bicarbonates)
• Lowering water pH
• Preventing nutrient precipitation
• Stabilizing micronutrients
• Optimizing nutrient uptake
• Increasing solubility
• Protecting Fe and Zn from oxidation

To manage these processes effectively, growers commonly use strong mineral acids (like nitric, phosphoric, sulfuric) and organic acids.

Why Acids Are Essential in Hydroponics

Most irrigation sources, particularly well water, contain high alkalinity, meaning they resist pH change.

High alkalinity causes:

• Nutrient lockout
• Precipitation of Ca, Mg, Fe
• pH drift in reservoirs
• Increased demand for chelated micronutrients
• Reduced fertilizer efficiency

Common Acids Used in Hydroponics & Fertigation

Table 1. Comparison mineral and organic acids.

How to Choose the Right Acid for Hydroponic pH Control

Selecting the correct acid depends on your plant stage, target nutrient profile, water alkalinity, fertigation system, and compatibility with your nutrient schedule. Below is a detailed overview of each acid type commonly considered for hydroponic pH adjustment.

Nitric Acid (HNO3) — Primary Choice for Vegetative Growth

Nitric acid is one of the most widely recommended acids for hydroponics, especially during the vegetative phase.

Benefits

• Provides nitrate nitrogen (NO₃⁻) — the cleanest and most stable form of N in hydroponics.
• Helps maintain stable pH in systems with moderate alkalinity.
• Does not introduce unwanted elements.

When to use

• Vegetative stage or leafy crops (lettuce, basil, greens).
• When your water source is low in nitrate and you want to boost NO₃⁻.
• When your alkalinity is moderate (40–150 mg/L CaCO₃).

Considerations

• Avoid during late flowering when extra N is undesirable.
• Highly corrosive — requires proper PPE and acid-safe storage.

Phosphoric Acid (H3PO4) — Best for Flowering and Fruiting Crops

Phosphoric acid is typically used in flowering and fruiting stages where phosphorus plays a critical role in energy transfer, bud development, and root metabolism.

Benefits

• Adds plant-available phosphorus (P).
• Effective for reducing pH in low to moderate alkalinity water.
• Often used when growers want to avoid increasing nitrogen levels.

When to use

• Bloom and fruiting phases (tomatoes, peppers, strawberries).
• When nutrient formulations already contain minimal P and small additions are beneficial.

Considerations

• Can cause calcium phosphate precipitation if used in concentrated stock tanks together with calcium salts (always separate A/B).
• Less effective at very high alkalinity.

Sulfuric Acid (H2SO4) — Industrial-Scale and High-Alkalinity Neutralization

Sulfuric acid is commonly used by commercial growers because of its low cost, strong buffering ability, and consistent pH reduction.

Benefits

• Adds sulfate (SO₄²⁻) — a safe and essential secondary nutrient.
• Extremely effective for neutralizing high alkalinity water (>150 mg/L CaCO₃).
• Ideal for greenhouses, large irrigation systems, and fertigation injectors.

When to use

• Large-scale operations or growers using high-alkalinity well water.
• When a strong, economical acid is required.

Considerations

• Concentrated H₂SO₄ is dangerous to handle — never recommended for small hobby setups without industrial-grade PPE.
• Excessive sulfate accumulation can occur in recirculating systems if used aggressively.

Hydrochloric Acid (HCl) — Not Recommended for Routine Nutrient Adjustment

Hydrochloric acid is generally avoided for pH Down in hydroponics because it introduces chloride ions, which can accumulate and harm plants.

Uses

• Primarily used for cleaning, descaling, and removing calcium carbonate deposits in irrigation equipment, emitters, drippers, pipes, and storage tanks.
• Sometimes used in emergency cases when no other acid is available, but not ideal.

Why not recommended for fertigation

• Chloride (Cl⁻) can quickly reach phytotoxic levels.
• Can destabilize nutrient chemistry over time.
• No nutritional benefit (unlike nitric, phosphoric, or sulfuric acids).

Organic Acids — Biological, Organic, and Sensitive Systems

Organic acids are mild, environmentally friendly, and compatible with organic hydroponics, living systems, aquaponics, and microbial-rich substrates. However, they are significantly weaker than mineral acids. Below is an expanded overview of each commonly used organic acid:

Acetic Acid (C2H4O2) — Vinegar-based pH Down

Pros

• Readily available, safe, and easy to handle. -Useful in small systems, home hydroponics, or organic setups.

Cons

• Very weak — requires large doses.
• Instability leads to pH drift due to microbial breakdown.
• Adds acetate, which can stimulate microbial growth (good or bad).

Lactic Acid (C3H6O3) — Microbe-Friendly Acid for Living Solutions

Pros

• Stronger than acetic acid, relatively stable.
• Supports beneficial microbes due to its biological compatibility.
• Suitable for bioponic or probiotic systems.

Cons

• Can become food for bacteria → biofilm buildup if not managed.
• Not strong enough for high-alkalinity water.

Formic Acid (CH2O2) — Fast-Acting but Niche Use

Pros

• More potent than most organic acids.
• Effective pH reduction with lower volumes.

Cons

• Rarely used in hydroponics due to handling hazards.
• Risk of phytotoxicity if overdosed.

Propionic Acid (C3H6O2) — Anti-Microbial Acid

Pros

• Has antimicrobial properties — reduces pathogens and mold.
• Occasionally used in systems prone to biofilm.

Cons

• Not commonly available in hydroponic-grade purity.
• Weak pH stability in recirculating systems.

Citric Acid (C6H8O7) — Popular Organic pH Down with Caution

Pros

• Very common in hobby hydroponics.
• Compatible with organic certifications.
• Easy to dissolve and handle.

Cons

• Can chelate micronutrients (particularly Fe³⁺ and Ca²⁺), causing nutrient lockout over time.
• Encourages microbial growth.
• Weak buffer capacity.

Table 2. How to choose the right acid by growing system and plant stage.

Acid Dose Calculation Made Simple

Maintaining stable pH in hydroponics is critical — but accurately calculating how much acid you need is far from trivial. To do it manually, you must account for:

• Water alkalinity (HCO₃⁻ or CaCO₃)
• Initial and target pH
• Acid type, purity, and dissociation strength
• Tank or system volume
• Water temperature, which affects reaction rates
• Whether your system is open or recirculating, influencing how fast pH drifts
• And many other subtle factors that change how acids behave in solution

That's exactly why we built a tool that handles all the chemistry for you.

Try the Growing Farm Acid Dose Calculator

A fast, precise, and intuitive way to calculate the exact acid dose your system needs.

What the calculator provides

• Nitric acid (HNO₃)
• Phosphoric acid (H₃PO₄)
• Sulfuric acid (H₂SO₄)
• Hydrochloric acid (HCl)
• Organic acids: Acetic, Lactic, Formic, Propionic, Citric

What the calculator gives you

• Exact mL of acid required for your tank or reservoir
• Automatic adjustment for acid concentration (%)
• Precise calculation of added nutrients (NO₃⁻, P, SO₄²⁻)
• Example calculation to help understand

Whether you're adjusting a 20-liter bucket or managing a commercial fertigation system, the Growing Farm acid dose calculator makes dosing accurate, safe, and effortless.

Conclusion

With the right acid and proper dosing, growers can achieve:

• More stable nutrient solutions
• Better nutrient uptake
• Reduced precipitation and clogging
• Stronger, healthier plant growth

To simplify dosing, use the Growing Farm Alkalinity Adjustment & pH Down Calculator for precise and safe adjustments.

For situations where your water is too soft or your pH tends to drop, you can use our Growing Farm Alkalinity Adjustment & pH Up Calculator to safely increase alkalinity using potassium-based buffers.

Calculate Your Acid Dose Instantly

Use the Growing Farm Acid Dose Calculator to safely and accurately calculate the amount of acid needed to adjust pH or neutralize alkalinity.

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