Dosing technique
In terms of
simplicity, properly formulated 1-parts stand alone. Apart from the
convenience of only needing one bottle, there are also virtually no dosing
rules governing their use - provided sufficient pH buffering capacity is
available. On the contrary,
the success of 2 & 3-part nutrients is very dependant upon dosing
technique (Fig 3.5):
+
Adding concentrated nutrient prematurely to too little water:
With 2 and 3-part nutrients, the “parts” are kept separate for good reason
– mix these together in concentrated form (or in too little water) and you
will see why (Fig 3.1). A white precipitate will form and, depending on the
formulation, this can happen well within a minute or so. Try this for
yourself – mix an equal volume of each part in a glass, undiluted. The
precipitate you can see is typically a combination of calcium sulphate and
calcium phosphate. Now, add excess water and see if it will dissolve.
The longer you delay dilution, the more difficult (or impossible)
dissolution becomes. Along with poor pH control, this is a main cause of
the white precipitate in nutrient tanks. Therefore to prevent this,
always add the majority of water before adding any nutrient.
Additionally, always stir well before each subsequent part is added.
+
Order of addition:
The addition sequence of each nutrient ‘part’ can affect nutrient
stability, particularly if the water has high alkalinity.
“Alkalinity” (bicarbonate & carbonate) is that component of natural waters
that causes high pH. Adding the nutrient dose to high alkalinity
water can decrease the stability of several nutrient species (including
calcium, sulphate, iron, copper, manganese, zinc). Therefore,
instead of pre-adjusting the pH of make-up water (an often very difficult
task), it is preferable to first add that ‘part’ of the nutrient that
lowers pH the most. This will be the ‘part’ that contains the
phosphate. In 2-part nutrients this is usually part ‘B’. Note
that the ‘part’ without any phosphate will impart relatively little effect
on pH. Secondly, it usually contains the iron which is highly
unstable at pH levels much above ~6.5. Note, in 3-part nutrients the
phosphate is sometimes dispersed acr
oss
2 bottles. Therefore, determine which contains the highest
concentration of phosphate, and add that first.
+
Add
equal amounts of each part:
If using a 2 or 3-part nutrient, avoid “roughly measuring” out the
nutrient dose. The “law of limiting factors” shows that an excess of one
nutrient species does not compensate for deficiencies in another. In the
case of a 2-part, ‘under’ dosing part ‘B’ for example, could cause a
deficiency in over half the nutrients required (i.e. P, K, S and all of
the trace elements excluding iron). This problem certainly applies to
1-part nutrient’s however, mathematically speaking the problem is
compounded with 2 & 3-parts because the target dose is roughly one-half to
one-third (respectively) of what it would otherwise be if using a 1-part.
As a consequence, the likely ‘percentage error’ is much greater. Also
note, for this same reason, the potential error is greatest for smaller
tank volumes i.e. due to smaller target dose rates.
On-going
maintenance
The nutrient’s
pH
buffering capacity is a function that manufacturers can incorporate to
ensure on-going ease of use.
Overview: Ease
of use
Dosing technique is critical for maximizing the performance of a 2 or
3-part. For fast and easy dosing, use a highly buffered, well balanced
1-part. Otherwise, if choosing between 2 & 3-parts, ensure pH buffering
capacity is a key selection criteria.
Next
Section...
