pH
indicators are undoubtedly the simplest and most reliable method of
measuring nutrient pH. Although they will not distinguish between, for
example, a pH of 5.2 and 5.3, ‘wide range’ indicators with good colour
resolution can be:
+ Fast and user friendly
+ Extremely accurate and reliable
+ Economical
In comparison, pH meters require constant
up-keep (i.e. cleaning, calibrating and correct storage), but even then
may not give reliable readings (see “Accuracy Problems with pH Meters”).
pH indicators work on the principle that the
colour produced by the particular dye used in the indicator formulation is
dependant on the pH of the solution (Fig 1.3).
Experience shows if you are aiming to adjust
pH to 5.5 (orange) then an accuracy of +/- 0.2 is achievable. Because of
their fundamental accuracy, reliability and easy of use, wide range pH
indicators are the preferred method for measurement of pH in nutrient
solutions.
Note that pool and aquarium pH indicators are usually not suitable because unlike Flairform's indicator, they
do not operate below pH 6.
Taking pH readings
Step 1. Before measuring the pH
ensure that the nutrient is well stirred, especially after pH UP and DOWN
are used. This is one of the most common mistakes made when testing pH
(or conductivity). Also, ensure that the sampling container is clean.
Step 2. Using the sampling vial,
remove a small sample of nutrient from the nutrient reservoir, add a drop of
the indicator, mix, then compare the final solution colour with those on
the colored reference chart.
Step 3. If the pH is not between
5.0 and 6.5, adjust it
immediately.
