You’ll read and hear about the use of “TDS,” Total Dissolved Solids, or Nitrogen PPM (parts per million) as control factors for feeding your plants. So how are you supposed to know what values you have?
Fertilizer labels don’t give the complete picture, as the “N-P-K” values are not reported in a straightforward manner, but in terms of N, P2O5, and K2O. This simple fertilizer TDS calculator takes those factors into account.
Note: These figures refer to the contribution of the major components only, so any minors or trace elements in the fertilizer will add to the TDS, as will any solids dissolved in your water. For example, Dyna Gro “Grow” formula is labeled as 7-9-5, which yields an N-P-K contribution of 199 ppm at one teaspoon per gallon, but if you add the other ingredients in that complete formula, the total contribution jumps up to 235 ppm.