The amazing truncheon ec meter from blue lab uses flashing lights to show the ec, cf and ppm readings. Truncheons are very accurate, reliable. Why are ppm, tds, ph. and ec important? A: Ppm and tds are abbreviations that represent the concentration of elements in a solution or atmosphere. Ppm is short for parts per million and tds for total dissolved solids. Ec (electro conductivity) is another form of measurement for tds. Ph is a measure of acidity or alkalinity which dictates plant uptake of particular elements. Q: What is the suggested ph. range for my hydroponic system and soil plants? A: Hydroponic and soil gardens differ in the fact they both need different ph. ranges for nutrients to be made available for plant absorption. Maintain a ph. between 5. 0 and 6. 5 for hydroponic gardens and 6. 0 to 7. 0 for soil applications.