Aqua Medic Ocean Runner 3500 Operation Manual - Page 11

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5. Feeding with Denimar: without Deniballs: 1 tablet/day.
6. From time to time: measurement of nitrite and nitrate concentrations in the oulet of
the Nitratereductor
Options
With a redox potential control, the function of the Nitratereductor can be optimised
and the reliability can be increased.
The optimal working point of the Nitratereductor can be determined by a
measurement of the redox potential.
Denitrifikation and redox potential
The redox potentialist ia a parameter, which can be measured electronically. The
value is a measurement for the equilibrium between reducing and oxidising reactions
in the water.
The redox potential in the aquarium itself is kept at plus 200 - 400 mV ( Millivolt) This
high redox potential indicates, that oxidation reactions dominate over reduction
reactions. Oxidation reactions are biochemical reactions, where a substance is
oxidised, e.g. by oxigen.
A negative redox potential indicates the absence of oxigen and is lethal for most
aquarium inhabitants.
The biochemical conditions in the Nitratreductor differ completely from the
aquarium:Nitrate has to be reduced to nitrogen gas. This is only possible if there is
no oxigen 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 under - 300 mV, all the nitrate is reduced. The bacteria start then to use
sulphate. This is a very undesired process because the end product of this reaction is
Hydrogensulfide. Hydrogensulfide (H
S) is toxic and smells very bad like fouling
2
eggs.
Therefore it is important, to keep the Nitratereductor always in the right redox level.
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 tabs, you should keep the flow rate constant and vary
the food sulpply. If you work with Deniballs, you should vary the flow rate.
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