Balance the hardness
and alkalinity
Problems with high pH seem to occur
most often in ponds where total alkalinity
(the amount of bicarbonate and carbonate
in the water) far exceeds water
hardness (the amount of calcium and
magnesium in the water). For example,
it is common for freshwater prawn
ponds at the Mississippi State University
aquaculture unit in Starkville
to have high pH in late spring. The
groundwater supply for these ponds has
a hardness of about 30 mg/L as CaCO3
and an alkalinity of about 90 mg/L. An
even wider disparity between hardness
and alkalinity is found in many
other waters, particularly those in the
southeastern coastal plains where many
groundwaters have alkalinities exceeding
150 mg/L and hardness values of
less than 10 mg/L.