Aqua Medic Marin 1000 Mode D'emploi page 19

- Feeding with Denimar: without Deniballs: 1 spoonful/day.
- Operation without redox control: from time to time, measurement of nitrite and nitrate
concentrations in the tank and outlet of the Nitratereductor is necessary.
7. Options
By a redox potential control, the function of the Nitratereductor can be optimized and the reliability
can be increased.
Denitrification and redox potential
The redox potential ia 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 a few hundred mV (Millivolt). In sea water
aquaria, the value should be between 300 and 440 mV. 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
livestock.
The biochemical conditions in the Nitratereductor differ completely from the aquarium: Nitrate has
to be reduced to nitrogen gas. A low or even negative redox potential is necessary. Here, 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 then start to use sulphate. This is
an undesired process because the end product of this reaction is Hydrogensulfide. Hydrogensulfide
(H S) is toxic and smells very bad like fouling eggs.
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Therefore, it is important to keep the Nitratereductor always in the right redox level.
Control of 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.
When feeding Denimar powder: the flow rate should be constant. If the redox potential falls below
-300 mV, don't feed at all. If the redox potential exceeds -50 mV, just double the dosage until it
falls again.
If you work with Deniballs, you should vary the flow rate. But don't increase the flow rate as you
like since then the outflowing water could contain Hydrogensulfide. If the flow rate is very slow the
redox potential falls to a value beneath –400 mV but the occurred Hydrogensulfide will be oxydized
in the aquarium immediately so there would be no danger for the livestock nor odour.
Control of flow rate when working with the dosing pump
By using a mechanic timer and program 15 minutes running time and 15 to 45 minutes break.
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