Two suppliers both report low EC coco peat. One says EC 0.4 mS/cm. The other says EC 0.8 mS/cm. Neither is misleading you—they are simply using different measurement methods. The 1:5 dilution and 1:1.5 dilution protocols produce substantially different numerical results from the same substrate, and confusing them leads to poor sourcing decisions and unexpected crop problems.
What Is EC and Why Does It Matter in Substrate?
Electrical Conductivity (EC) measures the concentration of dissolved ions in a solution. In the context of coco peat, it tells you how much soluble salt is present in the substrate before any nutrient solution is added. High starting EC means the substrate contributes its own salt load to the root zone—reducing your headroom for crop nutrition before osmotic stress begins.
For hydroponic crops, you want the substrate EC as low as possible before planting so that your nutrient programme is the only variable influencing root zone EC. A clean, low-EC substrate gives you full control. A high-EC substrate introduces an uncontrolled background EC that is hard to account for precisely.
The 1:5 Dilution Method
The 1:5 method (also written as 1:5 v/v or soil:water 1:5) involves mixing one volume of dry substrate with five volumes of distilled or deionised water. The mixture is agitated, allowed to equilibrate, and then filtered. EC is measured in the extract.
Because the substrate is heavily diluted, the resulting EC numbers are lower. A substrate that reads 0.4 mS/cm using 1:5 is not “cleaner” in absolute terms than it looks—the reading is simply diluted by a factor of approximately 3.5 to 5 relative to a more concentrated extraction.
The 1:5 method is widely used by substrate manufacturers and is the standard method used by most Indian and Sri Lankan coco peat exporters when providing CoA documentation.
The 1:1.5 Dilution Method
The 1:1.5 method (substrate:water 1:1.5) uses a much smaller volume of water relative to substrate. It more closely reflects the actual moisture content of the substrate in a hydroponic system during the growing season. This means it produces significantly higher EC readings from the same substrate.
The 1:1.5 method is preferred by many European hydroponic research bodies and is commonly referenced in Dutch growing guides. A substrate reading 0.4 mS/cm on the 1:5 method will typically read 1.2 to 2.0 mS/cm on the 1:1.5 method—a difference that is significant when evaluating suitability for sensitive crops.
Approximate Conversion Between Methods
| EC (1:5 method) | Approximate EC (1:1.5 method) | Suitability |
|---|---|---|
| < 0.3 mS/cm | < 1.0 mS/cm | Excellent — all crops including sensitive varieties |
| 0.3 – 0.5 mS/cm | 1.0 – 1.8 mS/cm | Good — suitable for most commercial crops |
| 0.5 – 0.8 mS/cm | 1.8 – 2.8 mS/cm | Moderate — pre-leaching recommended |
| > 0.8 mS/cm | > 2.8 mS/cm | High — not suitable for direct hydroponic use |
Note: the conversion factor between methods is not a fixed multiplier. It varies by substrate type, pith-to-fiber ratio, and the specific ion profile present. The table above provides approximate guidance only. Where precise comparison is needed, measure the same sample using both methods.
Rise Substrates CoA standard: We report EC using the 1:5 dilution method. Our finished substrate targets EC below 0.5 mS/cm (1:5). This is measured per batch and included in the Certificate of Analysis. If your team uses 1:1.5 as your internal standard, expect readings approximately 3–4× higher from the same substrate—in the range of 1.2–2.0 mS/cm at 1:1.5, which is commercially acceptable for most high-value crops.
Which Method Should You Use?
Use whichever method your lab or growing team uses consistently, and hold your suppliers to reporting in the same method. The critical point is not which method is “correct”—both are valid—but that you are comparing like with like when evaluating supplier CoAs.
When requesting substrate from a new supplier, always ask: which dilution method was used to generate the EC figure in your CoA? If they cannot answer, the figure is unreliable.
pH and EC Together
EC is only part of the starting substrate picture. pH must be measured alongside EC, as the substrate pH interacts with your nutrient solution to shift the effective pH in the root zone during the first days of the crop cycle.
Rise Substrates targets a pH range of 5.8 to 6.2 in the finished substrate. This aligns with the optimal nutrient availability range for most hydroponic crops and minimises pH correction requirement at crop establishment. Both pH and EC are reported per batch in our standard CoA documentation.