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The safe pH range for
freshwater aquatic life is
6.5-9.0 pH units
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Sudden pH "shocks," or changes, even
within this range can also harm fish
and should be avoided.
Effects of high pH on fish.
The effects of high pH on fish may
include: DEATH; damage to outer
surfaces like gills, eyes, and skin;
and an inability to dispose of
metabolic wastes.
High pH may also increase the toxicity
of other substances. For example, the
toxicity of ammonia is ten times more
severe at a pH of 8 than it is at pH
7.
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How
can I measure pH?
pH measurements may be made with:
 The pH test strips are
easy and inexpensive to use. All you
have to do is dip the test strip into
the liquid and the change in color on
the strip will correspond with the pH
(see photo to right).
A portable pH meter is more expensive,
however, it will provide a finer
resolution in the pH measurement, if
the person operating it is
knowledgeable in its use. The use of a
pH meter also requires additional
equipment and supplies such as
calibration standards.
Both pH test strips and pH meters are
available from scientific and chemical
supply companies (check the yellow
pages for companies serving your
area).
Is
there any way to treat high pH?
A liquid with a high pH can be
"neutralized" or returned to the safe
range for fish in a number of ways. For
example, an acid can be added. However,
great care must be taken when using
acids because it is very easy to
"overshoot" the neutral range and
change the pH to a very low pH which
can also kill fish (see The
pH of some common substances).
Alternatively, one can bubble gaseous
carbon dioxide through the liquid or
put "dry ice" (frozen carbon dioxide)
into the high pH material.
The active treatment of high pH wastes
is more appropriate for fixed
facilities such as concrete ready-mix
plants or large construction sites
where reliable control equipment can be
installed. Fisheries and Oceans does
not advocate the active treatment of
wastes at job sites. In those
circumstances, the most reliable way to
prevent environmental harm is to
control the waste waters by collecting
them and treating them off-site.
It is important to note that just
filtering concrete wash-water or
putting it into a settling pond (such
as might happen at a construction site)
WILL NOT treat the high pH. The
components that cause the high pH are
still there in dissolved form, and the
pH will still be high enough to kill
fish in a matter of minutes.
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CONCRETE
WASH-WATER IS VERY CLOUDY
 Portland cement is made
up of very fine particles. Concrete
wash-water is basically a slurry of
these fine particles in water. If a
concrete delivery truck or exposed
aggregate driveway is washed down into
a street drain, a large load of these
fine particles, also called suspended
sediments when in water, can be
delivered into a fish-bearing waterway.
The cloudiness is the result of these
particles scattering the light as the
light passes through the mix.
The picture at the right shows a
deposit of fine sediments into a creek
in Delta, B.C., from tile grout
wash-water dumped into a street
drain. Fish gills were coated
with the fine particles and the gravel
substrate was clogged (see below).
Fine sediments can:
Clog
fish gills
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Fish
get oxygen from the water that
passes over their gills. If the
gills get covered with fine
sediments, the oxygen cannot pass
from the water into the gill
tissues and the fish will
suffocate and die.
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Smother habitat
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If the spaces between gravel
particles are filled in,
incubating eggs will not get
enough oxygen and the insects
that fish eat will be smothered
and their living space
obliterated.
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Impair feeding ability
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Salmon are visual predators. If
the water they are feeding in is
cloudy, the fish will not be able
to see their prey.
 The graph to the
right shows the results of a
study of the ability of salmonids
(a group of fish that includes
salmon and trout) to capture prey
in varying degrees of cloudy
water. To view the full-sized
version of this graphic click on
the thumbnail, then to return to
this page, use your browser's
"Back" button.
In clear water (turbidity = 0
NTU*) the fish were able to
capture 100% of the prey, while
in cloudy water (turbidity = 60
NTU), the fish were able to
capture only 5% of the prey in
the test tank. (*NTU =
nephelometric turbidity
units)
(Graph adapted from: Berg, L.
1982. The effect of exposure to
short-term pulses of suspended
sediment on the behavior of
juvenile salmonids. In: G.
Hartman (ed.). Proceedings of the
Carnation Creek workshop, a 10
year review. Feb. 24-26, 1982,
Malaspina College, Nanaimo,
B.C.)
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The following table summarizes the
findings of a study of wash-water produced from
the cleaning of concrete delivery trucks. Two
main issues are highlighted by these
results:
Portland
cement (the active ingredient of concrete, as
well as mortar and tile grout) is the
ingredient that kills fish. When it
dissolves in water it forms calcium hydroxide
(Ca(OH)2), a highly alkaline
substance, and as a result produces a very high
pH (~12 pH units at 25°C) liquid.
This is why concrete wash-water has a pH that
is deadly to fish.
