cycl
beginner’s corner
per liter of solution. Again, seemingly
redundant language aside, it really is
just another way to measure the concen-
tration of a solution. First, moles (mol)
are calculated as a fraction of actual
mass of the solvent over the atomic
mass of that molecule. So, for example,
if you have 100 grams of solute that you
know is made up of magnesium sulfate
(MgSO 4 ), you would divide 100 by 120
to get 0.83 mol. The figure 120 comes
from the molecular mass of magnesium
sulfate, which is calculated from the
atomic mass of magnesium at 24,
sulfur at 32, and four atoms of oxygen
at 16 apiece, for a total of 120 g/mol.
From there, molarity is calculated from
moles divided by volume in liters and
displayed in M.
DOSING
In hydroponics, the EC
of MOST NUTRIENT
SOLUTIONS ranges
from 0.0-1.6, depending
on stage of growth.”
So, if your nutrient solution measures
in at 1.2 S on your EC meter, you
would multiply that by 500 to get
600 ppm. From there, you can
compare your results with that of
your feed schedule to determine
whether to dilute, intensify, or leave
your solution as is. American-based
manufacturers typically use the ppm
500 scale in their literature, whereas
European manufacturers tend to use
the ppm 700 scale. When in doubt, it is
best to verify before calculating and
subsequently dosing nutrients.
MOLARITY
Technically speaking, molarity (M)
indicates the number of moles of solute
94
grow cycle
If you are dosing your nutrients the
old-fashioned way by hand, you will
need your nutrient monitoring device
on deck continuously monitoring the
solution. When starting with a fresh
batch of reservoir water, fill it up to just
below the total fill line, leaving five to 10
per cent of the capacity as room to add
more water should your solution become
too concentrated. Typically, nutrient
manufacturers will suggest a dose
rate to theoretically achieve the proper
strength when in solution. If you have
multiple parts to add, dose them out in
a pipette, garden syringe, or volumetric
flask at the suggested rate on your
feed chart. Add each part one at a time,
being careful not to mix the separate
parts in undiluted form, as a precipitate
will form starting at the micro level,
which represents the early stages of
nutrient lockout. Eventually, this would
become a visible mass of rock that is
obviously unabsorbable. Once you add
the recommended doses, take a reading
with your meter. If the target strength
is within acceptable range, you’re all
set. If the reading comes in too hot, this
is when you would add more water
slowly while observing the reading on
your meter. Once reached, your solution
is now ready. On the flipside, if your
solution measures too low, you will want
to slowly add more nutrient until the
target strength is achieved.
Understanding how to read your meter,
take a measurement, and adjust the
levels in unison is important to boost
productivity. Maximizing potential lies
in the nitty gritty, and a prerequisite is
simply understanding the fundamen-
tals. Find a way that you understand,
stick with it, and be able to convert it
inside and out so you can start to get to
know your plants on a different level.