Electrical
conductivity (EC) can be used to compare the relative overall nutrient
concentration of different brands. This is done by measuring the EC value
of the nutrient when diluted 100 fold (10ml into 1,000ml) with distilled
water. To do this, add the following volumes to 1,000ml (1.05 Qrt) of
distilled water*:
+
1-parts: 10ml of nutrient.
+
2-parts: 5ml of part ‘A’ + 5ml of part ‘B’.
+
3-parts: Collect 10ml in
accordance with the ratio of parts used to achieve a given formulation
type e.g. 10ml of ‘bloom’ formulation may be comprised of 4ml part ‘A’ +
4ml part ‘B’ + 2ml part ‘C’.
Typically, the ‘best’ 2 & 3-parts yield
between 2.4 and 2.8mS (cF 24 to 28). Comparably, “slurry” type 1-part’s
can far exceed 3.0mS (cF 30) - see Graph 3.2.
*For accuracy, use a finely graded
pipette (or equivalent device) for measuring out the nutrient.
Comment regarding accuracy: Because the conductivity of different mineral salts varies, this
method does contain a degree of error. The error depends on how much the
ratio of nutrient species in the different brands vary from each other,
together with the type of mineral salts used. For example, judging a PK
additive against a full spectrum bloom formulation would not be a fair
comparison because phosphorus shows relatively low activity with
conductivity electrodes and therefore a conductivity measurement would
under estimate the PK specification. However, when comparing solutions of
similar nature (e.g. bloom versus bloom), it is probably the easiest and
quickest way of obtaining a good estimate of relative nutrient
concentration.
