Aqua Medic NR 400 Manuel D'instructions page 13

2. Recirculation pump: The recirculation pump has to be controlled regularly for clogging. The
pump housing has to be opened and the magnet with the needle wheel removed. Both is
cleaned under fresh water and re-mounted.
3. Cleaning: If the bacterial biomass has increased after some years, the Bactoballs can be
removed, cleaned with aquarium water and filled in again.
4. Renewal of Deniballs: The Deniballs have to be refilled/replaced once per year.
5. Feeding with Denimar: 1 tablet/day.
6. From time to time, measurement of nitrite and nitrate concentrations in the outlet of the
Nitratereductor.
9. Options
With a redox potential control, the function of the Nitratereductor can be optimized and reliability
can be increased.
The optimal working point of the Nitratereductor can be determined by a 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 because the end product of this reaction is Hydrogensulfide. Hydrogensulfide (H
and smells very strange like fouling eggs. 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.
Controlling the Nitratereductor NR 400
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 (Denimar tablets)
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
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 feeding rate.
They can only be determined by measurements of nitrite and nitrate concentrations in the filter or
by measurements of the redox potential.
The pump makes noise: If the pump housing contains air or gas, this causes a strange 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 housing of the pump has a small hole where air and gas
can escape. If this hole is blocked, it has to be cleaned with a needle.
S) is toxic
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