I think you mean Ec or tds. Slightly different but tests for the same thing. Its for hydro and coco growers. It stands for electroconductivity. Measures solids in your water, pure water is non conductive but the more disolved solids in the water raises the conductivity. Dissolved solids are basically minerals which effects your ph and nutrient requirements.
Tds is total Dissolved solids, different unit of measurement but tests for the same thing.
