When
to adjust pH
The working nutrient pH should be checked at
the following times:
1. When working nutrient solutions are
first made.
2. After the addition of top-up water
or additives - especially if they are highly alkaline.
3. In re-circulating systems, pH should
be checked on a daily basis because the uptake of water and nutrients
causes pH to change (Fig 1.10).
It is best to adopt a pH maintenance regime
that prevents pH from getting too high. If pH is too high for a long
enough period of time, the resultant precipitate usually cannot be
re-dissolved (Fig 1.2).
How to minimize pH fluctuation
1. Use a nutrient brand that is highly
pH buffered, particularly when
using highly alkaline water.
2. Supply at least 10 litres (2.5 gal) of
nutrient for each large plant. Failure to do this will magnify pH
(and EC) fluctuations, especially during hot and dry weather where water
uptake and evaporation are excessive. Note, to avoid excess water uptake
and evaporation, keep air temperature below 30oC (86oF)
and relative humidity above 50%.
How to adjust pH
Step 1. Measure the pH: Use
either a liquid pH indicator, or an
electronic pH meter. Before measuring the pH,
ensure that the nutrient is well stirred and that the sampling container
is clean.
Step 2.
Choosing a target pH: Note, it is inconvenient and unnecessary to hold pH
at a single point value. Therefore, choose a target pH that minimizes the
amount of pH maintenance:
+ If your pH tends to continuously rise
(the most common trend), then at each adjustment reduce the pH to about
5.0 using pH Down. This will give you a much larger pH "safety" margin
than if adjusting to, for example, 5.8.
+ If pH tends to continuously fall, at
each adjustment increase the pH to about 6.0 using pH Up.
Step 3. Adjusting the pH: Add a
small amount of pH Down / Up*. Then stir well and check pH. Repeat this
process until the target pH is achieved.
* Important: Pre-dilute
the dose into ~1 litre (or at least 100 fold) of water before adding to
nutrient, then rapidly stir the nutrient as you add this mixture.
Failure
to do this may cause permanent precipitation of essential nutrients. Also,
if accidental overdosing to above 6.5 occurs, reduce the pH back to below
6.0 as quickly as possible using pH Down.
