13
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 200 - 400 mV (Millivolt). This high redox potential
indicates that oxydation 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 Sulphur-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!
Control of the Sulphur–Nitratereductor:
The Sulphur-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 flow rate should be decreased. The
bacteria in the Sulphur Nitratereductor produce high amounts of sulphuric acid. This acid is
neutralised by the Hydrocarbonate to form Calciumcarbonate. The result may be the accumulation
of Calcium in the aquarium water (more than 800 ppm) and a decrease of the alcalinity. It is
recommended to determine the alcalinity of the seawater from time to time and adjust it with
supplements (Aqua Medic Reef Life Calcium, Buffer tabs). Regular water changes are recommended
to avoid a too high build up of the Calcium and Sulphate concentrations.
9.
Failures
Problems with the denitrification are mostly caused by wrong adjustion of the flow rate. They can
only be determined by measurements of the nitrite and nitrate concentrations in the filter or by
measurements of the redox potential.
-
The pump produces noise: If the pump housing contains air or gas, this causes a strong 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.
-
Nitrite in the outlet of the filter: If the outlet of the filter contains high amounts of nitrite, the
flow rate is too high: – reduce the flow rate.
-
Nitrate in the outlet of the filter: High residual concentrations of nitrate often occur together
with high nitrite values.
Caution
! Most nitrate tests are disturbed by high nitrite
concentrations! In this case, the redox potential is also too high. Increase feeding rates,
decrease flow rate.
10.
Warranty
Should any defect in material or workmanship be found within 12 months of the date of purchase
AB Aqua Medic GmbH undertakes to repair or, at our option, replace the defective part free of
charge – always provided the product has been installed correctly, is used for the purpose that was
intended by us, is used in accordance with the operating instructions and is returned to us carriage
paid. The warranty term is not applicable on the all consumable products. Proof of Purchase is
required by presentation of an original invoice or receipt indicating the dealer’s name, the model
number and date of purchase, or a Guarantee Card if appropriate. This warranty may not apply if
any model or production number has been altered, deleted or removed, unauthorised persons or
organisations have executed repairs, modifications or alterations, or damage is caused by accident,
misuse or neglect. We regret we are unable to accept any liability for any consequential loss.
Please note that the product is not defective under the terms of this warranty where the product,
or any of its component parts, was not originally designed and / or manufactured for the market in
which it is used. These statements do not affect your statutory rights as a customer. If your AB
Aqua Medic GmbH product does not appear to be working correctly or appears to be defective
please contact your dealer in the first instance. Before calling your dealer please ensure you have
read and understood the operating instructions. If you have any questions your dealer cannot
answer please contact us Our policy is one of continual technical improvement and we reserve the
right to modify and adjust the specification of our products without prior notification.
AB AQUA MEDIC GmbH - Gewerbepark 24 - 49143 Bissendorf/Germany
- Technical changes reserved – 08/2009