Compounds & Phosphate
Various nitrogen compounds formed in the aquarium are generated
from biochemical processes including the breakdown of proteins and
waste products from aquatic animals. The principal nitrogen compounds
of concern to the aquarium hobbyists are ammonia, nitrite, and nitrate.
Ammonia is the most toxic product formed in water. It originates
from the decomposition of nitrogen-containing organics such as plants
and food. Sources of ammonia in the aquarium water are the fish,
other organisms, and decaying food.
Ammonia exists in two chemical forms in water: a unionised
form (NH3) and an ionised form (NH4+). The combination of these
two forms is termed total ammonia. Both exist in water, but the
proportion of each type is dependent on the pH, temperature, and
other factors. The unionised form is extremely toxic to fish. The
higher the pH of the water, the higher the concentration of toxic
Chronic sublethal concentrations of ammonia in aquariums
indicate that there is a serious problem that can be related to
various factors, including overcrowding, filter malfunction, or
overfeeding. Fully functional and properly conditioned aquariums
should have no detectable concentrations of ammonia.
Ammonia can easily be detected using commercially available
test kits. Some kits will express the result as ion, while others
will express the result as ammonia-nitrogen. As a general recommendation,
the unionised form of ammonia must not exceed 0.01 mg/L in aquariums.
Always follow the manufacturer's instructions exactly to
obtain the correct readings for ammonia, regardless of the method
for expressing the results.
During the development of nitrifying bacteria in the filter
bed, the bacteria will transform ammonia into another form of nitrogen
called nitrite. Nitrite is the intermediate step in the nitrogen
cycle in the conversion of ammonia to nitrate. The highest concentrations
occur during the initial establishment of the filter bed. Once the
filter bed is established, it is often impossible to detect any
nitrite. Though nitrite is less toxic than ammonia, it is still
somewhat toxic to water animals because it binds with blood cells,
which prevents the normal uptake of dissolved oxygen.
The concentration of nitrite is also determined with a test kit.
The concentration should not exceed 0.1 mg/L (parts per million,
or ppm) as nitrite ion. Continual high concentrations during the
initial conditioning period indicate that the nitrogen cycle is
Nitrate is formed from the chemical conversion of nitrite
in the aquarium. It is far less toxic than nitrite and considerably
less toxic than ammonia. Although it has been thought that nitrate
had little effect on aquatic organisms, recent research has shown
that high concentrations of nitrate can adversely affect the growth
and survival of water animals in the long term.
It is recommended that nitrate not exceed 50 mg/L (ppm),
and preferably should not exceed 20 mg/L (ppm). The lower limit
is often impossible to achieve in some aquariums. Nitrate levels
can be tested with commercially available test kits.
Phosphate, like nitrate, accumulates in aquarium water over
time. Phosphates can become a problem if allowed to exceed allowable
concentrations. Excessive phosphate concentrations can affect the
health of invertebrates as well as contribute to the undesirable
growth of algae. The excessive algae growth on rock in reef aquariums
will prevent the desirable coralline algae from developing the concentration
of phosphate should be monitored in aquariums. The testing of phosphate
in reef aquariums is essential as part of the routine water quality
It is important to note that phosphate occurs in both inorganic
and organic forms. Many test kits only measure the inorganic form,
also known as orthophosphate. Therefore, you can make an erroneous
assumption that no phosphate is present if you are using a test
kit that measures only orthophosphate. You should check with your
pet store concerning the correct type of phosphate kit to purchase.
The source of phosphate originates from three primary sources:
utilisation of food by the aquarium animals, decay of excessive
food, and activated carbon and municipal water. You must be careful
about not overfeeding, as this contributes to the build-up of phosphate.
Make sure that whenever you purchase carbons they are phosphate-free.
Most premium brands on the market will note on the label that the
product does not contain phosphate. Tap water should also be tested
to ascertain if phosphate is present. If your tap water always contains
phosphate, you should consider using deionized water for your aquarium.
Phosphate levels should generally not exceed 0.2 mg/L for
aquariums containing fish.