TDS stands for Total Dissolved Solids, which are the total amount of minerals, salts or metals dissolved in water.
They are basically mobile charged ions floating in a nutrient solution and determine the electrical conductivity (EC) of water. TDS and EC measurements are used to determine the nutrient value of your solution in a hydroponics setup.
TDS meters actually use a calculation from EC to garner their results. They estimate TDS levels based on the electrical conductivity of the water. A TDS meter will calculate the EC level and then convert it to a TDS measurement. There are many variables to be considered when conducting these measurements, in particular the factor that varying metals, minerals and salts will conduct electricity at varying levels.
TDS is calculated by converting the Electrical Conductivity by a factor of approximately 1.0 times the EC [sometimes as low as .05, depending upon the levels].
Typically, the higher the level of EC, the higher the conversion factor to determine the TDS, and the higher the level of Total Dissolved Solids . ppm (parts per million) is the scale used to measure.
TDS (Total Dissolved Solids). Micro-Siemens is the scale used to measure EC (Electrical Conductivity). A TDS reading of 1 ppm would indicate there is 1 milligram of dissolved solids per kilogram of water.
To estimate a solutions TDS, you can utilize a meter that measures the Electric Conductivity (EC) of a solution, and convert the number to TDS in parts per million (ppm). Some meters will do this conversion for you.
Nutrient ions [Salts, minerals, metals] have an electrical charge, a whole number, usually a positive or negative 1, 2, or 3. EC is a measurement of all those particles in the solution that conduct electricity. The greater the nutrient ion quantity in a solution, the more electricity that will be conducted by it. A solution with a measurement of one siemens allows a single ampere of electric current to pass through it per volt of electric potential.
TDS readings primarily give you a range, pinpoint accuracy is not essential. TDS levels should be within a certain range and do not , nor can they be maintained exactly.
There are no meters that will indicate what elements are in your solution, or in what quantity.
They can't even tell you if the elements within the parts per Million are useful or harmful elements to your plant. For a nutrient solution to do it's intended job , all the mineral elements within it need to be in balance. The best way to keep your solution in balance is not only via diligent monitoring, but by a regular regimen of flushing and replenishing water and nutrients as they are depleted. See: How often should hydroponic nutrient solutions be changed ?
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