Hydroponic Nutrient Calculator

The 7 salts behind every hydroponic formula

Every one of the 125 formulas in this calculator is mixed from the same seven raw salts. Commercial nutrient brands sell these pre-diluted in branded bottles; buying them raw costs a fraction of the price and lets you match the ratio to the crop and growth stage instead of accepting one generic blend. Here is what each one actually does.

Parts A, B and C are not a marketing convention — they exist because these salts cannot all share a container. Calcium must be kept away from sulphates and phosphates in concentrated form, which is why the calculator splits every formula three ways.

Why nutrients are mixed in three parts

In a full reservoir the salts are dilute enough to coexist. In a concentrate they are not. Calcium ions from calcium nitrate bind with sulphate ions from magnesium or potassium sulphate to form calcium sulphate — gypsum — and with phosphate from MKP to form calcium phosphate. Both are close to insoluble. They drop out as a white sludge, and the calcium and phosphorus locked inside are gone from the solution for good.

The practical consequence is a fixed order of operations. Fill the reservoir first, then add each part to that full volume one at a time, stirring until clear before the next goes in:

1. 1

   Part A — Calcium Nitrate, Potassium Nitrate, Fe-EDTA — into the full reservoir. Stir until clear.

2. 2

   Part B — MKP, Potassium Sulphate, Magnesium Sulphate — into the same reservoir, never into the Part A bottle.

3. 3

   Part C — The micronutrient mix, last. Grams are small, so dissolve it in a little water first.

4. 4

   pH — Only now adjust pH, then confirm EC with a meter.

EC and pH targets by crop type

EC (electrical conductivity, in mS/cm) measures how much dissolved salt is in your water — it is the single most useful number in hydroponics. pH governs whether those dissolved salts can actually be absorbed. The calculator returns an exact target for your specific plant and age; these are the broad bands those targets fall within.

Two rules apply across every crop. Start low and climb: seedlings take a fraction of the strength a fruiting plant needs, which is why the calculator asks for plant age and scales the formula for you. And keep pH in the low-to-mid 5s to 6s — outside that window iron and phosphorus lock out and the plant shows deficiency symptoms even though the nutrient is sitting right there in the water.

On PPM: it is a conversion from EC, not a separate measurement, and there is no universal factor. US and Hanna meters typically use 500, EU and Truncheon meters 700. This calculator reports 1 mS/cm ≈ 650 ppm, following Howard M. Resh, Hydroponic Food Production (7th Ed.). Always check which scale your meter uses before comparing numbers with another grower.

Five mistakes that ruin a nutrient batch

Most nutrient problems are not formula problems. They come from how the solution is mixed and maintained.

Which systems these formulas work with

All of them. A nutrient formula describes water chemistry, not plumbing, so the same grams per litre apply whether you run deep water culture, NFT, Kratky, Dutch buckets, ebb and flow, or drip into coco and clay pebbles. What changes between systems is how fast the solution is consumed and how quickly EC drifts — recirculating systems need checking more often than run-to-waste. Measure EC and pH regularly whichever you use, and top up with plain pH-adjusted water between full changes.