15
9.
Maintenance
1.
Control the flow rate: The flow rate through the filter has to be checked regularly. The optimum
is at approx. 0.5 to 1 l/hr. This has to be readjusted from time to time.
2.
Recirculation pump: The recirculation pump has to be controlled regularly on clogging. The
pump housing has to be opened and the magnet with the needle wheel removed. Both is cleaned
under fresh water and mounted again.
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 during the first 4 - 6 weeks.
6. From time to time, measurement of nitrite and nitrate concentrations in the outlet of the
Nitratereductor
.
10.
Options
With a redox potential control, the function of the Nitratereductor can be optimised 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 oxydising 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 oxidation reactions dominate over reduction reactions. Oxydation reactions
are biochemical reactions, where a substance is oxydised, 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
2
S) is toxic 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.
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 (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.
