Hydroponic nutrients are not mysterious formulas—they are carefully balanced solutions of water-soluble mineral salts.
This Lab Note explains why commercial nutrients are sold as Part A and Part B, how to prevent precipitation (“knockout”), and how to formulate your own professional-grade concentrates from technical salts.

Summary

1. Introduction to Hydroponic Nutrients

In soil, bacteria, fungi and earthworms gradually break down organic matter into water-soluble mineral ions that plant roots can absorb. In hydroponics, we bypass this biological process by dissolving those same mineral ions directly into water.

This is an important distinction.

Plants do not absorb fertilizer granules, crystals, or chemical compounds. They absorb dissolved ions. Nitrogen is taken up primarily as nitrate (NO₃⁻), potassium as K⁺, calcium as Ca²⁺, magnesium as Mg²⁺, and so forth. If the nutrient is not dissolved in water, the plant cannot access it.

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2. Why Hydroponic Nutrients Come in Two Parts

One of the first questions every grower asks is why hydroponic nutrients are almost always sold as Part A and Part B.

Surely it would be easier to put everything into one bottle?

The answer lies in chemistry rather than horticulture.

Commercial nutrients are supplied as highly concentrated stock solutions. A five-litre concentrate may eventually produce hundreds of litres of irrigation solution once diluted into the reservoir. At these high concentrations, certain mineral ions become chemically incompatible with one another.

The primary offender is calcium.

If Calcium Nitrate is mixed directly with Monopotassium Phosphate (MKP) or Magnesium Sulfate (Epsom Salt) in concentrated form, the dissolved ions rapidly combine to produce insoluble calcium compounds. Instead of remaining dissolved, they form a white sludge that settles to the bottom of the container, consisting of insoluble Calcium Phosphate and/or Calcium Sulphate. Those nutrients have effectively been knocked out from the solution.

For this reason, commercial manufacturers simply separate the incompatible ingredients.

Part A generally contains:

• Calcium Nitrate
• Iron chelates
• Compatible nitrate salts

Part B generally contains:

• Monopotassium Phosphate (MKP)
• Magnesium Sulfate
• Potassium salts
• Trace element package

The underlying mineral salts remain exactly the same.

The bottles simply provide greater flexibility.

NOTE: You do get single component ‘hydroponic’ nutrients – but these are falsely advertised “Fertigation” fertilizers – and designed to be added to soil. As in soil you get high concentration of calcium salts, so they remove CaNO₃ from the “Hydroponic” nutrient,

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3. The Chemistry of “Knockout”

Throughout the STS Lab Notes we use the practical term Knockout.

Chemists refer to the process as precipitation, while growers often speak about nutrient lockout. Although related, these terms describe slightly different aspects of the same problem. When incompatible ions meet at high concentrations they chemically react to form compounds that are almost insoluble in water. A common rule of thumb we apply is above 10 000PPM [20ms/cm].

Instead of remaining available to the plant, they literally fall out of solution – The nutrients have been knocked out of the liquid.

One of the most common reactions occurs between calcium and phosphate, and/or sulphate:

The chemistry has already happened. Fortunately, the solution is simple:

Keep incompatible ions separated while concentrated.

Only allow them to meet after they have been diluted into the final reservoir.

This explains why hydroponic nutrient concentrates are almost always stored separately but can safely coexist once diluted into hundreds of litres of irrigation water. It also explains why mixing concentrated nutrients together before adding water is one of the quickest ways to ruin an expensive batch of fertilizer.

This same principle also applies when making your own concentrate from dry mixes:

• Water first.
• technical hydroponic salts second.
• Never the other way around.

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4. The Building Blocks — Hydroponic Technical Salts

Every commercial hydroponic nutrient ultimately begins with a surprisingly small collection of raw materials known as technical salts. These are highly purified, completely water-soluble mineral compounds manufactured specifically for fertigation and hydroponic applications.

Unlike conventional agricultural fertilizers, technical salts contain very little insoluble filler or coating material. They dissolve rapidly, leave minimal residue and provide nutrients in precisely known concentrations.

Each technical salt contributes one or more essential plant nutrients. For example:

• Calcium Nitrate supplies both calcium and nitrate nitrogen.
• Potassium Nitrate contributes nitrogen together with potassium.
• Monopotassium Phosphate (MKP) provides phosphorus and potassium.
• Magnesium Sulfate (Epsom Salts) supplies magnesium together with sulfur.

Plants respond to elements, not products.

Refer to #113 STS Lab Note for a rundown of the various elements and functions of macro- and micro-nutrients.

Element	Primary Role
Nitrogen	Leaf and stem growth
Phosphorus	Root development and energy transfer
Potassium	Water regulation and fruit quality
Calcium	Cell walls and new growth
Magnesium	Chlorophyll production
Sulfur	Proteins and enzymes
Iron	Chlorophyll synthesis
Manganese	Photosynthesis
Zinc	Growth hormones
Copper	Enzyme activation
Boron	Cell division
Molybdenum	Nitrogen metabolism
Chlorine	Osmotic balance

A tomato plant has no concept of brand names. It simply absorbs nitrate ions, potassium ions, calcium ions and magnesium ions from whatever source makes them available. Whether those nutrients originated from an expensive imported concentrate, a locally mixed technical salt formulation, organic vermicompost or a professionally engineered commercial product makes no difference to the plant.

The objective of every hydroponic nutrient is therefore remarkably straightforward:

Deliver every essential mineral element in a water-soluble form, at the correct concentration, while preventing incompatible ions from reacting before they reach the root zone.

That simple principle has underpinned hydroponic nutrient formulation for nearly a century and remains the foundation upon which virtually every commercial nutrient on the market is built today.

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5. Making Hydroponic Nutrient Concentrates

Once you understand why nutrients are separated into two parts, preparing your own concentrates becomes surprisingly straightforward.

The first rule is simple:

Never mix concentrated Part A and Part B together.

Another important consideration is concentration.

More concentrated is not always better.

There is a practical limit to how much mineral salt water can hold before crystals begin forming or instability develops during storage. Commercial manufacturers spend considerable effort balancing concentration against long-term shelf stability. While it is tempting to produce extremely concentrated stock solutions to save storage space, moderate concentrations are generally easier to manage and considerably more forgiving.

Storage conditions also matter.

Keep concentrates sealed, protected from sunlight, and stored in a cool environment. High temperatures accelerate chemical degradation, while evaporation gradually changes concentration over time. Properly prepared concentrates remain remarkably stable provided incompatible salts have been separated correctly.

For most growers, accuracy matters more than complexity. A carefully measured nutrient mixed consistently every time will outperform an elaborate formulation mixed differently every week. Hydroponics rewards repeatability.

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6. Commercial Formulations — Standing on the Shoulders of Giants

Modern hydroponic nutrient companies often market their products as proprietary formulations developed through decades of research.

While every manufacturer may make small adjustments for particular crops or growing conditions, nearly all commercial nutrient systems trace their ancestry back to two landmark formulations.

Nearly fifty years later, Dutch greenhouse researcher A. Sonneveld refined these ratios for intensive commercial vegetable production. His work adjusted the balance between several macro- and micronutrients to better suit greenhouse green leavy crops.

Although their elemental ratios differ slightly, the philosophy behind both formulations is identical.

• Provide every essential nutrient in sufficient quantity.
• Maintain appropriate elemental balance.
• Keep every nutrient dissolved and available to the plant.

Nearly every commercial hydroponic nutrient sold today—from hobby kits to industrial greenhouse formulations—can trace its chemical ancestry to these two formulations.

This is worth remembering – Commercial nutrients are not mysterious inventions.

They are carefully engineered variations of well-established scientific principles that have been publicly available for decades.

The value lies in convenience, quality control and ease of use—not secret chemistry.

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7. Practical DIY Nutrient Recipes

With an understanding of technical salts, concentrate preparation and nutrient compatibility, preparing your own hydroponic nutrients becomes entirely achievable.

Most leafy vegetables such as lettuce, spinach and herbs perform exceptionally well on relatively mild nutrient solutions with electrical conductivities between approximately 1.5 and 2.0 mS/cm.

Heavy-feeding fruiting crops including tomatoes, peppers and cucumbers generally require stronger nutrient solutions, often operating between 2.2 and 3.0 mS/cm, depending on the growth stage and environmental conditions.

Working from Scratch here is a list of products you can use, with their relative nutrient components and strengths, and mass of each for 1000L nutrient @ 2 mS/cm. So to make you will dissolve Calcium Nitrate in 10 liters water [Part A = 1] and the rest all in separate 10L water concentrate [Part B = 2 to 11]:

1. Calcium Nitrate (895.3 g)
   • Nutrients: 15.5% Nitrogen (N), 19% Calcium (Ca)
   • Concentration (g/kg): 155 g/kg Nitrogen (N), 190 g/kg Calcium (Ca)
2. Ammonium Nitrate (86.7 g)
   • Nutrients: 34% Nitrogen (N)
   • Concentration (g/kg): 340 g/kg Nitrogen (N)
3. Potassium Nitrate (885 g)
   • Nutrients: 13% Nitrogen (N), 44% Potassium (K)
   • Concentration (g/kg): 130 g/kg Nitrogen (N), 440 g/kg Potassium (K)
4. Potassium Phosphate Monobasic (262 g)
   • Nutrients: 0% Nitrogen (N), 52% Phosphorus (P), 34% Potassium (K)
   • Concentration (g/kg): 0 g/kg Nitrogen (N), 520 g/kg Phosphorus (P), 340 g/kg Potassium (K)
5. Magnesium Sulfate (Epsom Salt) (498.5 g)
   • Nutrients: 9.1% Magnesium (Mg), 13% Sulfur (S)
   • Concentration (g/kg): 91 g/kg Magnesium (Mg), 130 g/kg Sulfur (S)
6. Sequestrene 330 (18.9 g)
   • Nutrients: 10% Iron (Fe)
   • Concentration (g/kg): 100 g/kg Iron (Fe)
7. Manganese Sulfate (1.5 g)
   • Nutrients: 31% Manganese (Mn), 18% Sulfur (S)
   • Concentration (g/kg): 310 g/kg Manganese (Mn), 180 g/kg Sulfur (S)
8. Zinc Sulfate (692 mg)
   • Nutrients: 35.5% Zinc (Zn), 17% Sulfur (S)
   • Concentration (g/kg): 355 g/kg Zinc (Zn), 170 g/kg Sulfur (S)
9. Copper Sulfate (0.17 mg)
   • Nutrients: 25% Copper (Cu), 12% Sulfur (S)
   • Concentration (g/kg): 250 g/kg Copper (Cu), 120 g/kg Sulfur (S)
10. Borax (Laundry Grade) (2.8mg)
    • Nutrients: 11% Boron (B)
    • Concentration (g/kg): 110 g/kg Boron (B)
11. Sodium Molybdate (0.12mg)
    • Nutrients: 39% Molybdenum (Mo)
    • Concentration (g/kg): 390 g/kg Molybdenum (Mo)

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8. Conclusion — Understanding the Chemistry Gives You Independence

Hydroponic nutrients are often presented as proprietary products wrapped in colourful labels and impressive marketing claims.

In reality, they are carefully balanced mixtures of water-soluble mineral salts following chemical principles that have been understood for generations.

Once you understand why nutrients are separated into Part A and Part B, how precipitation reactions occur, and which technical salts provide each essential element, commercial nutrient bottles lose much of their mystery.

That does not mean there is anything wrong with buying ready-made nutrients. Commercial formulations save time, are professionally manufactured and remain an excellent choice for many growers.

However, understanding the chemistry gives you something more valuable than a recipe.

It gives you independence.

You can troubleshoot deficiencies with confidence.

You understand why knockout occurs instead of simply being told to “never mix the bottles.”

You can compare commercial products objectively instead of relying on marketing claims.

And if circumstances require it, you have the knowledge to formulate your own nutrients from readily available technical salts.

That, ultimately, is the purpose of this Lab Note.

Not to convince you to stop buying nutrients.

But to understand exactly what is inside the bottle—and why it works.

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Socratic Questions

1. how to mix raw fertigation salts for hydroponics
2. difference between hoagland and sonneveld nutrient formulas
3. how to prevent calcium sulfate chemical knockout
4. diy technical grade hydroponic nutrient recipe weights
5. commercial tomato nutrient formulation ppm targets