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9. Options
With a redox potential control, the function of the Nitratereductor can be optimized and the
reliability can be increased.
The optimal working point of the Nitratereductor can be determined by the measurement of the
redox potential.
Denitrification and redox potential
The redox potential is a parameter which can be measured electronically. The value is a
measurement for the equilibrium between reducing and oxydizing reactions in the water.
The redox potential in the aquarium itself is kept at plus 300 - 440 mV (Millivolt). This high redox
potential indicates that oxydation reactions dominate over reduction reactions. Oxydation reactions
are biochemical reactions where a substance is oxydized, e. g. by oxygen.
A negative redox potential indicates the absence of oxygen and is lethal for most aquarium
inhabitants.
The biochemical conditions in the Nitratereductor differ completely from those in the aquarium:
Nitrate has to be reduced to nitrogen gas. This is only possible if there is no oxygen dissolved in
the water.
The redox potential is low or even negative. The ideal range is between -50 and -250 mV.
If it exceeds -50 mV, the denitrification reaction may stop at the nitrite stage!
If it falls below -300 mV, all the nitrate is reduced. The bacteria then start to use sulphate. This is a
very
undesired
process
Hydrogensulfide (H
S) is toxic and smells very strange like fouling eggs.
2
If a little bit of Hydrogensulfide is entering the aquarium, this is not critical. It is immediately
oxydized to sulphate. The closed version of the Nitratereductor causes no problems with bad smell.
Control of the Nitratereductor
The Nitratereductor can be controlled by the rate of feeding or the flow rate of water:
If the redox potential exceeds -50 mV or even gets positive, the dosage of food can be increased or
the flow rate decreased.
If the redox potential sinks below -300 mV, the feeding can be reduced or the flow rate increased.
If you work with the Denimar -Powder, you should keep the flow rate constant and vary the food
supply. If you work with Deniballs, you should vary the flow rate.
10. Failures
Problems with denitrification are mostly caused by wrong adjustion of the flow and the feeding
rate. They can only be determined by measurements of the nitrite and nitrate concentrations in
the filter or by measurement of the redox potential.
- The pump produces noise: If the pump housing contains air or gas, this causes a strong noise.
In this case, the pump is pumping little or no water and its cooling is insufficient. The pump may
overheat and be destroyed. The plastic elbow at the pump outlet has a small hole where air and
gas can escape. If this hole is blocked, it has to be cleaned with a needle.
- Nitrite in the outlet of the filter: If the outlet of the filter contains high amounts of nitrite, the
feeding rate is too low. Increase the feeding or lower the flow rate. In most of those cases, the
redox potential is too high (more than -50 mV).
- Nitrate in the outlet of the filter: High residual concentrations of nitrate often occur together
with high nitrite values. Caution! Most nitrate tests are disturbed by high nitrite concentrations! In
this case, the redox potential is also too high. Increase feeding rates, decrease the flow rate.
- Hydrogen sulphide in the outlet of the filter: The filter smells like fouling eggs. In most
cases, the redox potential is too low. Reduce the feeding, check the flow rate and increase it if
necessary.
All manuals and user guides at all-guides.com
because
the
end
product
of
this
reaction
is
Hydrogensulfide.
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