Idiomas disponibles
Idiomas disponibles
1. Theory
What is Kalkwasser?
The addition of a saturated solution of Calciumhydroxide was the first method for supplying reef
aquaria with Calcium. Powdered Calciumhydroxide is stirred into tap or reverse osmosis water,
undissolved hydroxide settles down and the clear supernatant is slowly added to the aquarium.
This clear solution is called „Kalkwasser" or lime water. Because of its high pH of 12.4 a dripwise
addition is required to avoid a dangerous rise of the pH value in the aquarium. This solution
attracts carbondioxide from air. This results in the formation of calcium carbonate that is hardly
soluble and precipitates. The calcium content of the Kalkwasser decreases. If the pH value from
the Kalkwasser decreases from 12.4 to 12.2, the calcium content drops from 900 to 300
ppm. The entrance of carbon dioxide into the solution has to be avoided as far as
possible.
If you measure the carbonate hardness or alcalinity of a Kalkwasser solution, you will find a very
high value. This value is, however, not caused by bicarbonate or carbonate ions which can be used
by the corals but by hydroxide-ions. The hydrochloric acid in the alcalinity test cannot differ
between these substances. In the aquarium, the hydroxide reacts with dissolved carbondioxide to
-
form bicarbonate (OH
+ CO
= HCO
) – if dosed slowly. If you dose the Kalkwasser too fast,
2
3
hydroxide may react with bicarbonate to form calcium carbonate – which is almost unsoluble. As a
2+
-
-
result, the alcalinity drops (Ca
+ HCO
+ OH
= H
O + CaCO
). For this reason, it is
3
2
3
recommended to add Kalkwasser during the night when you find the lowest pH value and
the highest carbondioxide concentration.
An important advantage of the so-called "Kalkwasser-method" is the precipitation of phosphates.
By this process, almost unsoluble hydroxylapatite is formed:
3 Ca
(PO
)
. Ca(OH)
= Ca
(PO
)
(OH)
3
4
2
2
10
4
6
2
This substance will not dissolve under "normal" aquarium conditions.
2. Working principle of the reactor
The unit is filled with tap or reverse osmosis water and calciumhydroxide (Kalkwasserpowder,
approx. 2 cups). The internal stirrer is started and the insoluble calciumhydroxide forms a sediment
at the bottom. Here, it is mixed with inlet water. Now,you can pump water with a small external
pump (e. g. Niveaumat or dosing pump SP 3000) through the reactor. This pump is operated by
a level controller or a time switch. The water flowing into the reactor is enriched with calcium as it
is pumped through the calciumcarbonate sediment. As the flow rate is slow, the undissolved
calciumcarbonate settles and you always have a clear solution of calciumhydroxide at the outlet.
This principle allows a very compact construction. The reactor is hermetically sealed, carbon
dioxide can enter the reactor only with inflowing water. By this, an interval between 2 fillings of
several weeks is possible. This interval depends firstly on the calcium requirement of the aquarium.
For refilling the reactor, the used liquid is drained and fresh calciumhydroxide is added. Afterwards,
the reactor is filled with fresh water and the stirrer is started. If the solution has cleared up, the
unit is ready to go.
Inlet:
The Kalkwasserstirrer is only supplied with by top up water to replace evaporated water in the
aquarium. If the tap water is of good quality (low nitrate, phospate) it can be used. But we
recommend to treat tap water by a reverse osmosis unit, e. g. Aqua Medic Standard 90. This refill
water is placed in a reservoir (canister or glass tank).
Now, the inflow (7) can be connected to the reservoir via a suitable pump. We recommend to use a
peristaltic pump (dosing pump SP 3000) or Niveaumat with integrated level control.
Control:
We recommend to operate the Kalkwasserstirrer together with the electronic level control Aqua
Medic aquaniveau or Niveaumat. If water evaporates in the aquarium, it is replaced from the
reservoir via the Kalkwasserreaktor.
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