The other most tacit reason behind using grow media as alternative grow substrate are their chemical properties. pH (ions of Hydrogen), Cation Exchange Capacity (CEC) and Electrical conductivity (EC) are the major chemical properties to distinguish between.
pH value
The pH value will speak of the acidity or basicity of the growth media. In ideal conditions, pH of a grow media is estimated between 5.2 to 6.2 at 5.8 as saturation point.
It is known that, at the time of germination and root development, the pH level is slightly lower than the ideal (4.9-5.5) to make it convenient for the water alkaline from constant watering.
And eventually the pH level reaches its saturation point by the addition of fertilizers from time to time.
Cation Exchange Capacity (CEC)
The measure of ability of a grow media to absorb the exchangeable cations in feeds and provide them to plants while resisting leaching of nutrients in water run off.
Terms of CEC of growing media are expressed in meq/L and a perfect CEC ranges from 60-250 meq/L.
Generally, CEC is highly dependent on pH value, and higher the proportion of EC number (humic acid), higher the value of CEC.
Electrical Conductivity (EC)
The measure of the ability of grow media to carry electric charges within the molecule of water and nutrients. It is directly proportional to the amount of ions dissolved in water. Expressed in terms of mS/cm. For the sake of simplicity, the higher the EC, the stronger the ability of charge carriers.
The desirable EC value of an ideal grow media is between 1-2 cS/cm. During the germination and propagation phase it is estimated between 0.4-1.0 mS/cm.