10
Feeding:
The feeding has to be adjusted according to the nitrate loading of the aquarium. It can be controlled
with a redox probe (see options). In a normal loaded tank, one spoonful denimar-Powder per day is sufficient.
It is possible to feed several dosing spoons (up to 5 pcs.) at one time. The filter needs no feeding then for
several days.
After some time, a slimy bacterial biomass is formed in the Nitratereductor.
This a normal process. A high
bacteria population ensures a high removal rate of nitrate.
8.
Feeding with Deniballs
Aqua Medic Deniballs are made of a biodegradable plastic material. This plastic material is also produced
biologically - the raw material is produced by bacteria. This new plastic material is completely biodegradable. It
can be used by denitrifying bacteria in the Nitratereductor to remove nitrate. The Deniballs supply the surface
area and the food for the bacteria at the same time. This means that a Nitratereductor filled with Deniballs has
not to be fed for a longer period - up to one year. The quantity of Deniballs which are necessary for a
Nitratereductor depends on the loading of the tank. For a normal loading, 5 l are enough. The rest of the filter
is filled with the standard Bactoballs. The Deniballs need - especially in a saltwater tank - a longer period to
reach their full capacity.
9.
Maintenance
-
Controlling the flow rate: The flow rate through the filter has to be checked regularly. The optimum is at
approx. 10 l/h. This has to be readjusted from time to time.
-
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
re-mounted again.
-
Cleaning: If the bacterial biomass has increased after some years, the Bactoballs can be removed, cleaned
with aquarium water and filled in again.
-
Renewal of Deniballs: The Deniballs have to be refilled/replaced once per year.
-
Feeding with denimar: Without Deniballs 1 dosing spoon daily.
-
From time to time, measurement of nitrite and nitrate concentrations in the outlet of the Nitratereductor
has to take place.
10. 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 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 positive redox potential in the aquarium
itself is kept at a few hundred Millivolt. In the seawater tank, it 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 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.
