As hardy as our fish are, long exposure to poor water quality will
cause stress and disease. Unfortunately, we cannot rely on our
unaided senses to determine water quality — clear water is not
an indication of good water quality from our fish’s perspective.
Poor quality stresses our fish, which in turn causes their immunize
system to go down, which in turn makes our fish susceptible to
disease. In order to know if there is good water quality, it only
makes sense to test it periodically rather than wait for disease
systems to appear.
Fish waste and other organic debris are
the first steps of the nitrogen cycle, a series of events that
produces some of the compounds we test for — ammonia, nitrites,
and nitrates. Normally, we should test for PH, ammonia, nitrites,
and nitrates every week or two. Testing should be made more
frequently during periods of change in our ponds, such as spring
warming, new filter installation, major pond cleaning or repair.
PH indicates the ratio of hydrogen ions to
hydroxyl ions on a logarithmic scale from 0 (pure acid) to 14
(pure alkaline). Fish do best in water with a PH of 7.0 to
8.5. They can actually tolerate a wide range, but cannot
tolerate a rapid change. PH affects the free ammonia/ionized
ratio, with a higher PH resulting in a greater concentration
of free ammonia. To make things more complicated, algae and
other water plants can drastically change a pond’s PH from
night to day, due to a change in the amount of dissolved
carbon dioxide present in the water. We’re concerned about
rapid PH shifts not only because of the ammonia ratio, but
also because the fish are trying to keep their blood PH level
during these shifts, thereby causing stress. PH needs to be
- Ammonia introduced by fish waste and decomposing organic
debris, is the most toxic nitrogen compound. It is present in
two forms. Free and ionized. Free ammonia is the most toxic
and will cause death in very low concentrations. Problems
associated with non-lethal elevated levels of ammonia include
gill disease, dropsy and fainter. The higher the PH and the
temperature, and the lower the salinity or hardness, the more
toxic the ammonia. With a properly functioning biological
filter, the ammonia is usually zero.
- Nitrite is less toxic than ammonia, but still very toxic
as it inhibits the ability of the blood to carry oxygen.
Nitrite is oxidized into nitrate by nitrobacteria bacteria
living in the filter.
- Nitrate is the end product of the nitrifying phase of the
nitrogen cycle. It is much less toxic than either ammonia or
nitrite. It is how ever, a nitrogen compound that is the food
and fertilizer for algae. In nature, nitrate is absorbed by
water plants and is reduced into free nitrogen by anaerobic
bacteria living in the bottom silt. Hydrogen sulfide and
methane gas are given off as a by-product of the anaerobic
filtration. An oxygenated, clean pond will not have any
anaerobic bacteria present, so nitrates will accumulate in the
pond. Partial water changes of 1/10th per week will
flush out the accumulating nitrate.
- Dissolved Oxygen is usually only a warm weather concern,
as it is associated with water temperature and algae. However,
the larger the fish, the greater the oxygen demand. Low levels
of oxygen allows you to determine if your pond has the maximum
amount of oxygen for the temperature of the water.
- Salt Level Test -- pond fish actively maintain a natural
balance of electrolytes in their body fluids. Electrolytes
such as potassium, sodium, chloride, calcium, and magnesium
are removed from the water by chloride cells located in the
gills. These electrolytes are essential for the uptake of
oxygen and release of carbon dioxide and ammonium across gill
membranes. The lack of electrolytes can cause serious health
problems to the fish. During periods of disease and stress,
healthy gill function is disturbed. This can lead to the loss
of electrolytes through the gills, sometimes call osmotic
shock. Osmotic shock interrupts healthy gill function by
reducing the intake of oxygen and the release of carbon
dioxide and ammonium from the fish. Rock salt overfeeding can
lead to elevated nitrite levels especially in newly set up
ponds. The nitrite ion NO2 enters the gills and prevents the
blood from carrying oxygen resulting in nitrite toxicity. Rock
salt will temporarily block the toxic effects of nitrite while
corrective action is taken.
- A Pond Thermometer is important to check pond’s water
temperature to maintain fish on correct feeding schedule.
Testing gives you the information you need to ensure the best
possible conditions for your fish, as well as the information
to maintain water clarity.