Managing high pH in aquaculture
ponds is difficult and no specific management
practice is always successful.
Difficulties arise because the term “high
pH” describes not only a chemical
property, but also the outcome of many
interacting chemical and biological processes.
As a measure of water’s hydrogen
ion concentration, high pH can be
corrected simply by adding an acid to
increase that concentration. However,
“high pH” also describes the net result
of many individual processes that add
or remove carbon dioxide. Reducing pH
with an acid does not alter these processes
and, therefore, cannot address
the underlying causes of high pH. So
while adding an acid may temporarily
reduce pH, high pH will probably occur
again unless other environmental conditions
also change.
The long-term solution to high pH problems
in ponds is to alter pond biology
so that the net daily carbon dioxide uptake
is near zero. This can be done by
reducing photosynthesis or increasing
respiration. But changing the metabolism
of the pond community is difficult
because biological processes have con-
siderable “ecological momentum.” This
momentum is based upon a given set of
environmental conditions that strongly
favor a particular ecological outcome.
For example, when a newly filled pond
contains lots of nutrients, receives
bright sunshine and has warm water
temperatures, conditions strongly favor
the development of a biological community
that produces a high afternoon pH.
Altering those conditions to change the
outcome is difficult. In general, preventing
or managing around pH problems
will be more effective than trying to
correct problems after they occur.