Backyard Aquaponics
A place to discuss aquaponics

Had a discussion going about potassium chloride in the temp forum. So far no one piped in with any reason potassium chloride could not be used to salt for fish health.
I was also wondering if using potassium chloride might be easier on salt sensitive plants along with providing some extra potassium.
Just some thoughts.

EC, CF and TDS(ppm) - just what are they?

First of all lets dispel the myth that they are all the same sort of measure - they are not.

TDS(ppm) refers to the actual quantity of a salt or salts in solution (Total Dissolved Solids) whereas EC and CF refer to the electrical conductivity (ie how easily the solution passes an electric current).

Now, we can measure EC (CF) quite easily by passing a high frequency AC current through the solution but we cannot directly measure ppm.

EC is measured in mS/cm (milli Siemens per centi metre) and CF is measured in units 1/10 of a mS/cm so the conversion between CF and EC is 1 EC (mS/cm) = 10CF.

So what about measuring the EC and then multiplying the answer by a conversion constant to tell us what the ppm is.

Unfortunately, this cannot be done for the simple reason that the conversion constant for every salt is different.

Beware of meters that provide a read-out in ppm, they will only give a correct reading for one particular salt - usually sodium chloride.

This is unfortunate as sodium chloride has a very different conversion constant from most hydroponic salts and will therefore give a reading that has a very large error.

In fact TDS meters usually are calibrated to comply with one of three standards namely NaCl (1mS = 500ppm), 442 (1mS = 700ppm)and some have an imperical standard of 1mS = 650ppm).