Mixing Your Own Nutrient Solution From Raw Salts: A Worked Recipe, A/B Stocks and a Safe Mixing Order (Part 2 of 2)

AZ_Growshop_Asia · October 22, 2026, 7:07pm

This article turns raw fertiliser salts into a working nutrient solution. It covers a complete worked recipe, how to estimate EC before you mix and how to check the potassium–calcium–magnesium balance. It also covers chelated micronutrients, concentrated A and B stocks, the mixing order with a check after each step, and reservoir temperature in a hot climate. Every quantity comes from one formula: grams per litre = target ppm ÷ (10 × P). P is the percentage of the element in the salt, stated as the element itself, not as P₂O₅ or K₂O.

This is Part 2. Part 1: Mixing Your Own Nutrient Solution From Raw Salts: The ppm Arithmetic

A complete worked recipe

The recipe below only shows the method. It is a general-purpose solution, not a feed chart optimised for cannabis. The percentages are typical label analyses, converted to the elemental basis. Use the figures printed on your own bags.

Salt (analysis used)	g/L	N	P	K	Ca	Mg	S
Calcium nitrate (15.5% N, 19% Ca)	0.80	124	–	–	152	–	–
Monopotassium phosphate, MKP (22.7% P, 28.2% K)	0.22	–	50	62	–	–	–
Potassium nitrate (13% N, 38% K)	0.20	26	–	76	–	–	–
Magnesium sulphate heptahydrate (9.8% Mg, 13% S)	0.50	–	–	–	–	49	65
Potassium sulphate (41.5% K, 18% S)	0.15	–	–	62	–	–	27
Total (ppm)	1.87	150	50	200	152	49	92

Each cell is simply g/L × 10 × P. For example, MKP gives 0.22 × 10 × 22.7 = 50 ppm of P. Micronutrients (see below) are added on top.

What to do: rebuild this table in a spreadsheet using the analysis from your own bags. When the spreadsheet does the multiplication, you can spot a typing error before it reaches the plants.

Estimating EC before you mix

EC depends on how many electric charges the dissolved salts carry, not on their weight. A milliequivalent per litre (meq/L) is a unit that counts those charges. To convert, divide ppm by the equivalent weight, which is the atomic weight divided by the ion’s charge:

Potassium (K, charge 1): equivalent weight 39.1
Calcium (Ca, charge 2): 40.1 ÷ 2 = 20.0
Magnesium (Mg, charge 2): 24.3 ÷ 2 = 12.2

A widely used rule of thumb is EC (mS/cm) ≈ total positive ions (cations) in meq/L ÷ 10.

For this recipe:

K: 200 ÷ 39.1 ≈ 5.1 meq/L
Ca: 152 ÷ 20.0 ≈ 7.6 meq/L
Mg: 49 ÷ 12.2 ≈ 4.0 meq/L
Ammonium: about 0.6 meq/L. Fertiliser-grade calcium nitrate carries a small share of its nitrogen as ammonium.

The total is about 17.3 meq/L. So the recipe should add roughly 1.7 mS/cm on top of whatever your source water reads.

The negative ions (anions) give you a cross-check. Nitrate ≈ 10.1, sulphate ≈ 5.7 and phosphate ≈ 1.6 meq/L, about the same total as the cations. If the two totals match, the arithmetic is probably right. Real EC varies with the salt mix, so treat this only as an estimate. The meter has the final say.

The same rule lets you estimate each part on its own. That is useful for the mixing checks further down:

Part A (calcium nitrate): Ca 7.6 + ammonium 0.6 ≈ 8.2 meq/L, so about 0.8 mS/cm.
Part B (the other salts): K 5.1 + Mg 4.0 ≈ 9.1 meq/L, so about 0.9 mS/cm.

Checking the potassium : calcium : magnesium balance

Potassium, calcium and magnesium are all positively charged ions taken up by the roots. A large excess of one can reduce how much of the others the plant takes up. So it helps to see their ratio at a glance.

For this recipe, the ratio by ppm is 200 : 152 : 49, or about 4.1 : 3.1 : 1. By meq/L it is 5.1 : 7.6 : 4.0, or about 1.3 : 1.9 : 1. The recipe this method comes from gives no target ratio, so this article does not give one either.

What to do: work out the same ratio for a formulated product you trust, using the analysis on its label. Then compare it with your own recipe. Recalculate the ratio every time you swap one salt for another, because a single swap can shift all three numbers.

Micronutrients and chelated iron

Iron (Fe), manganese (Mn), zinc (Zn), boron (B), copper (Cu) and molybdenum (Mo) are needed in tiny amounts. As a rough guide, typical hydroponic recipes contain about:

Fe 1–3 ppm
Mn 0.3–0.8 ppm
Zn 0.05–0.3 ppm
B 0.2–0.5 ppm
Cu 0.02–0.1 ppm
Mo 0.01–0.05 ppm

For a small batch, these amounts are too small to weigh without an analytical balance, a laboratory scale far more precise than a kitchen or jewellery scale. Most people who mix at home buy a ready-made chelated micronutrient blend and dose it with the same formula.

Iron must be chelated. A chelate is an organic molecule that wraps around the metal ion. It keeps the iron dissolved and available to the roots. Iron salts without a chelate precipitate as the pH rises. Choose the chelate to match your pH:

Chelate	Keeps iron available up to about
Fe-EDTA	pH 6.5 (fine for hydroponics run at 5.5–6.0; the cheapest)
Fe-DTPA	pH 7.5
Fe-EDDHA	pH 9 (for high-pH media or hard water; the most expensive)

Published cut-off values differ a little between sources, but the order is always the same. Here is an example with the formula. A 13% Fe-EDTA, dosed to 2 ppm of Fe, needs 2 ÷ (10 × 13) = 0.015 g/L.

Light breaks iron chelates down. That is another reason to keep the reservoir dark.

What to do: check the pH of your source water and your medium, then pick the cheapest chelate that still covers that pH.

Why Part A and Part B are kept apart

In the final solution, every salt is dilute, so everything stays dissolved. In a 100× stock, every salt is 100 times stronger. At that strength, calcium meets phosphate or sulphate and they form solid calcium phosphate or calcium sulphate. These solids settle to the bottom.

When this happens, three things go wrong:

Calcium, phosphorus and sulphur sit at the bottom of the container instead of reaching the plants.
The final EC reads lower than expected, because the solids no longer carry current.
Solid particles can collect in pipes and drippers.

This is why calcium nitrate goes in Part A, and the phosphate and sulphate salts go in Part B.

How to check a stock:

Look at it. A good stock is clear, with no cloudiness or sediment. Shake it and look again.
Do a test dilution. Add 10 ml of A to 1 litre of your source water, stir, then add 10 ml of B and stir again. The EC should be about 1.7 mS/cm above the EC of the source water alone.
Interpret the result. A much lower reading points to one of three causes: precipitation, a weighing error or salt that never dissolved. Remake the stock rather than correcting the reservoir.

What to do: run this test dilution every time you make a new stock, and write the result on the container label.

Making 100× A and B stocks

Weighing grams of salt for every reservoir change is slow. The error is also largest on small batches. The standard fix is to make two concentrated stocks once:

Part A: the calcium nitrate, usually together with the iron chelate.
Part B: the phosphate and sulphate salts (MKP, potassium nitrate, magnesium sulphate, potassium sulphate) and the other micronutrients.

For a 100× stock of the recipe above, multiply each g/L figure by 100 and dissolve it in 1 litre of stock:

Part A: 80 g calcium nitrate (+ 1.5 g Fe-EDTA)
Part B: 22 g MKP, 20 g potassium nitrate, 50 g magnesium sulphate, 15 g potassium sulphate

To use the stocks, add 10 ml of A and 10 ml of B per litre of final solution. That is 1 litre of each per 100 litres. Potassium sulphate dissolves least easily of the salts in Part B. So check its solubility before you push the stock above 100×.

Label both containers clearly and store them in a dark, cool place. Never combine A and B undiluted.

Translator’s note: in a room at 30–35 °C, “cool” means the coolest shaded spot you have. Do not store stocks in sunlight or near grow lights. Use opaque containers, because light also breaks down the iron chelate in Part A.

Mixing order, and what to check after each step

Follow these steps in order. Each check tells you right away whether that step worked, so you can find a problem before the solution reaches the roots.

Fill the reservoir to its full volume with water first. Measure the EC and temperature of the water and write them down. This is your baseline for every later check.
If you mix from dry salt, dissolve each solid completely. Warm water speeds dissolving. Undissolved salt at the bottom of the tank makes the meter reading meaningless.
Add the first part (for example Part A) and stir. A submersible pump keeps the reservoir mixed while you work. Check: the water is still clear, and the EC has risen by roughly 0.8 mS/cm for this recipe.
Add the second part (Part B) and stir. Never mix the concentrates with each other first, above all calcium with phosphate or sulphate. Check: the water is still clear, and the EC is about 1.7 mS/cm above the baseline.
Add supplements last. Organic additives make EC readings unreliable. So add them only after the salt readings are where you want them.
Set EC first, then pH. pH takes longer to settle than EC, so mix thoroughly before you read it. Aim for roughly 5.5–6.0 in hydroponics (details in pH & EC). Do not chase every 0.1 change.
Dilute the pH Up or Down product first, then add it slowly while stirring. A small patch of high pH in the tank can precipitate calcium phosphate and iron. Check: after full mixing, the solution is still clear and the pH is stable.
Record everything. Write down the batch, date, target EC and pH, measured EC and pH, and water temperature.

Four general rules apply to every batch:

Start low and increase gradually. Every cultivar responds a little differently.
Keep the recipe simple. Do not try to add everything.
Replace the solution rather than chasing a deficiency. After several days of feeding, the nutrient balance in a reservoir drifts. If you suspect a nutrient problem, the usual right answer is a fresh solution, not more additives. See Nutrient Lockout in Cannabis.
If a check fails, stop and find the cause. Adding more of something rarely fixes a cloudy or low-reading tank.

Reservoir temperature in a hot climate

Keep the reservoir at 20–22 °C and keep light out of it. Algae then become much less of a problem. Warmer water holds less dissolved oxygen. An air pump can only raise oxygen to saturation, the maximum the water can hold at that temperature, and no higher.

Translator’s note: this point matters most in Southeast Asia. In a room without air conditioning, at 30–35 °C, a reservoir will never sit at 20–22 °C on its own. Warm nutrient solution holds less oxygen. That is exactly the condition in which Pythium, a water mould that attacks roots, and root rot take hold. Here, cooling the reservoir is not optional. This is the single biggest difference between running hydroponics in a temperate climate and in a tropical one.

The options, from cheapest to most expensive:

The minimum: insulate the reservoir, raise it off the warm floor and keep it out of the light. This slows how fast the room heats the water.
Use cooler space: place the reservoir inside an air-conditioned room, or in the coolest shaded corner you have.
For hot days and power cuts: put sealed bottles of frozen water into the reservoir. Do not add loose ice. Melting ice dilutes the solution and lowers the EC.
A water chiller holds the temperature steady. In October 2026, Thai online aquarium shops listed small chillers rated for about 100–160 litres at roughly 6,500–10,000 baht. Prices change. In a hot room, choose a unit rated above your reservoir volume.
Change the system if cooling costs too much. The options are compared in Running Hydroponics at 31 °C Reservoir Temperature.

Power cuts make the problem worse. When the power goes, the air pump and any chiller stop together. The warm water then loses oxygen with nothing to replace it. A battery-powered air pump, or a UPS (uninterruptible power supply, a battery unit that keeps devices running for a short time), keeps air flowing.

What to do: put a thermometer in your reservoir and record the water temperature at the hottest time of day for one week. Then pick the cheapest option above that keeps it at 20–22 °C. Check the temperature again whenever the power returns after a cut.

A checklist if you do this properly

A calibrated EC meter whose conversion factor you know. Without it, every ppm figure in your log is ambiguous.
A calibrated pH meter. Without it, you cannot tell whether the iron chelate and calcium are staying in solution.
A scale accurate to 0.01 g for the major salts. Use a pre-blended micronutrient mix unless you have an analytical balance.
Salts with a stated guaranteed analysis, from a supplier who will provide it. The formula is only as good as the percentage you enter.
Separate A and B stocks, never combined undiluted. This prevents precipitation.
A written recipe with the calculation shown. You can check it, and someone else can reproduce it.
Records: the batch, the date, target and measured EC and pH, and how the plants responded. Over several crops, these records show which changes actually helped.

Home salt mixing rarely fails because of the arithmetic. It fails because of undissolved salt, precipitated calcium, a meter on the wrong scale and a mislabelled bag.

Share what you found

If you have mixed from raw salts in Thailand, Vietnam or elsewhere in the region, please post below. Say which salts you could buy and what analysis was printed on the bag. Most useful of all, compare your measured EC with the estimate from the method above. The arithmetic on this page is simple. The open question is whether a bag of calcium nitrate bought here really contains what its label says. Only growers who have measured it can answer that.