9
2.
Theory
Nitrate is coming into the aquarium via 2 different ways:
- with the tap water, with every water change or with the replacement of the evaporated water
- by biological reactions in the aquarium
These biological reactions are responsible for the far most biggest part of the increase of the nitrate level.
How is nitrate produced in the aquarium?
When the animals are fed with dried, living or frozen food, proteinaceous substances get into the aquarium.
These are the basics of the diet for the animals. A big part of the nitrogen, from the food is, however, excreted
into the water. This nitrogen is metabolised by bacteria, living in the aerobic filter via the toxic intermediate
substances ammonium and nitrite to the less toxic nitrate. These biochemical reactions take place in the
presence of oxygen:
The bacterium Nitrosomonas oxydizes Ammonia to Nitrite, the bacterium Nitrobacter the Nitrite to Nitrate.
Am Oxygen ----- > N Oxygen -----> Nitrate
(Nitrosomonas) (Nitrobacter)
In most aquaria, nitrate is the endproduct of bacterial metabolism and accumulates in the water. Only higher
water plants and algaes are able to remove this nitrate from the aquarium water.
What is the effect of nitrate in the aquarium?
- Overfertilization/eutrophication: The aquarium is overfertilized, the algae growth increases and cannot be
controlled anymore.
- Toxic effects to the animals. Many invertebrate animals in sea water tanks are very sensitive to higher nitrate
levels.
3.
Working principle of the Nitratereductor
In the Aqua Medic Nitratereductor, the water is treated anaerobically. In the absence of oxygen, many bacteria
are able to use nitrate as a substitute for oxygen for their metabolism.
2 Nitrate ----> nitrogen gas + 3 oxygen
2 NO3 ----> N2 + 3 O2
The oxygen is used for metabolism, the nitrogen is excreted into the water. Nitrogen gas is a natural compound
of the water and totally harmless.
It is, however, necessary to increase the metabolism of the bacteria so that they can reduce enough nitrate. For
this reason, the nitrate removing bacteria have to be fed with organic substances. The food
denimar
contains
organic substances that can be used completely by the bacteria. The only waste product is CO
2
.
The flow rate through the Nitratereductor is very slow. This is the main difference to other aquarium filters
where the water is often treated once per hour or even more often. The water in the Nitratereductor
should
have a retention time of 4 hours. It is, however, sufficient to treat it once per week. If the filter is adjusted
correctly, the water leaves the filter nearly free of nitrite and nitrate.
4.
Description of the
Nitratereductor
The Aqua Medic Nitratereductor
consists of a reaction vessel (1) of 10 l volume. To provide surface material for
bacteria, the filter is filled with Aqua Medic
Bactoballs
(2). They create an ideal microclimate for denitrification.
To avoid dead zones, the water is recirculated internally in the Nitratereductor. A recirculation pump (7) is placed
in the top.
In denitrifying filters, especially in units where the water has to pass through a long way, it can occur that there
is no even flow in the filter. Zones with a very low redoxpotential are created where hydrogensulfide is produced
