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Salinity
Salinity refers to the amount of dissolved
salt per kilogram in your tank and it has
the unit of ppt (part-per-thousand). For example, 30 ppt means 30 g of chemical
dissolved in 1 kg of water. The natural sea
water has an average salinity level of 35
ppt. To prepare salt water for your tank,
follow the instructions on the package and
mix your salt with tap water in the portion
that you think is suitable for your tank.
Let the aqueous solution settle overnight
before use.
Importance of Salinity
There are many reasons for the unwanted alges
to grow in your tank; one of them is a low
salinity in your tank. However, the main
reason for keeping a stable salinity is related
to the saltwater fishes' osmoregulatory behavior.
There is usually a difference between the
salinity level in your aquarium and that
in the fish cells. If the salinity level
is higher in the aquarium than that in a
fish's cells, the surrounding water will
immediately start flowing into the fish cells.
Meanwhile, the fish tries to release its
excess salt to the ambient water in order
to stabilize the flow. This is called the
osmoregulatory behavior.
Osmoregulatory behavior refers to the constant
adjustment that the fishes must undertake
in order to maintain a balance between two
different salinity levels.
Osmoregulation raises a question for you
to decide if you should adjust the salinity
level for a new fish before you put it into
your own tank. This is because your local
pet shop's tanks may have a different salinity
level than your tank. It is wise to consult
with your local pet shop of any necessary
adjustment when you decide to buy a delicate
species. Although fishes have the ability
to adjust the most suitable salinity level
for itself, most fishes dislike a huge sudden
change in salinity, which can create stress
or even shock for them.
Measuring Salinity in Your Tank
Although salinity is usually described in
the unit of ppt, you usually do not get the
salinity reading of your tank in the ppt
unit directly. To measure the salinity, let
your hydrometer float in the water and take
the reading at the water surface level. The
reading that you will get is in the form
of 1.0XX. When you measure the salinity,
do not forget to mark down the water temperature.
Salinity varies with the water temperature
levels. We recommend that your tank's salinity level
should be kept roughly between 1.021 and
1.024 at 75 Fahrenheit. (If you are interested in the ppt value,
you can then use a conversion table to convert
the reading from your hydrometer at the particular
temperature to the corresponding ppt value.)
Since salinity is a critical element in your
tank, it is recommended to get accurate readings
using electronic instrument instead.
Picture of a Salinity Meter
This is a new picture of a Salinity meter.
Information added on Friday, July 14, 2000
7:19:00 PM
Although a simple hydrometer can measure
the salinity level of your tank quite easily,
specific gravity measurements (i.e. the 1.0XX
measurements), in general, are not very accurate.
(The accuracy of the hydrometers vary a lot
from different manufacturers.) The alternative
of measuring the salinity is to measure the
conductivity (S), the reciproal of resistance. This salinity
meter from PINPOINT makes use of such a relationship
between the conductivity and the salinity
to measure the salinity level accurately.
This salinity meter has a probe to be submerged
in the water and the corresponding reading,
in ppt value directly, will be shown on the screen
of the monitor. (The monitor must be sitting
outside the tank.) The bottle shown besides
the monitor is included in the kit to calibrate
the monitor before it is used. The solution
is of 53 mS. With the probe submerged in
a bucket containing the solution, you can
calibrate the monitor so that the reading
on the screen match the 53 mS. (You can calibrate
the monitor by tightening or loosing a screw
in the back of the monitor.) Since salinity
is a very important element to indicate the
well-being of your tank, we highly recommend
this simple-to-use salinity meter. (Also
included in the salinity kit is a conversion
table including the equivalent specific readings
and the ppt values.)
Information added on Friday, July 21, 2000
12:27:40 AM
Maintaining Salinity Level in Your Tank
Some people do not like to have a cover for
their tanks because they believe that the
glass top may weaken the intensity and quality
of the light. Some people, however, may have
a trouble of keeping their fish from jumping
out of the tank, and hence, they would like
to have a glass cover instead. In either
case, if your lighting system runs 10 hours
a day, evaporation can be an issue for your
tank. Evaporation disturbs the salinity level
of your tank. When the water is evaporated, the salt that
was originally dissolved is now released.
This increases the concentration of the salt
in your tank. You can use your hydrometer to decide the
amount of tap water needed to dilute the
highly concentrated saltwater.
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pH and pH Buffer
As we mentioned in the FAQ section, pH is
the most important element in your tank.
Inappropriate pH level is reflected by the
observation of your fishes becoming inactive
and staying at the bottom of the tank most
of the time. pH measures the acidic or basic reaction
of the water. In pure water, there are Hydrogen
(H+) and Hydroxide (OH-) ions. Pure water has a pH level of 7 which
indicates the presence of equal amount of
these two types of ions in the water. Natural
sea water, however, is basic (or alkaline)
and has a pH level of approximately 8.2.
This means that there are more Hydroxide
ions than Hydrogen ions in natural sea water.
The carbon dioxide produced in the process
of photosynthesis decreases the pH level
in the water. Therefore, the pH levels are
different in the "light" time (when
your lights are on) and in the night time
(when your lights are off).
pH Buffer as the Safety Device
pH buffer goes hand-in-hand with pH. Buffer capacity generally refers to the capability
of the sea water to recover and stabilize
to the level before any disruption. There are different types of buffer capability:
pH buffer and KH buffer. (We will deal with
KH buffer later.) The oxygen released in
the photosynthesis is consumed by the living
creatures in your tank and hence a balance
between the oxygen and carbon dioxide levels
is maintained. However, if the rate of photosynthesis
is higher than the rate of respiration, then
more carbon dixoide is produced. This drives
the buffer capability down because the excess
negatively charged ions are used up to counter-balance
the acid produced by carbon dioxide molecules.
If the buffer capability is exhausted, the
excess carbon dioxide drives the pH level
down quickly. Your tank can also lose its
buffer capability from the acids released
from the bacterial decomposition of the metabolic
wastes in the water.
So the buffer capability acts as a safety device
to absorb the constant changes of the pH
level in the water. It restores the pH level
as long as the capability is not exhausted.
Once it is exhausted, the pH level in your
tank will drop immediately and significantly
within days. It is always critical to maintain the buffer
capability in your tank at all time.
Maintaining your pH level
To maintain your pH level means to have the
amount of basic ions to neutralize the excess
acidic ions in the water. The neutralization
requires negatively charged ions for the
chemical reaction to happen. Among these
negatively charged ions, carbonate (CO32-) and hydrogen carbonate (HCO3-) ions are generally termed as the carbonate
hardness. Carbonate Hardness is a specific jargon to
refer to only the concentration of the carbonate
and hydrogen carbonate ions. That is, carbonate hardness excludes the
hydroixde ions (OH-) completely.
As you may have already guessed, there is
another type of buffer capability to describe
the acid-neutralizing capability contributed
by these two types of ions. This specific
type of buffer capability is called KH buffer. This, however, is where some people get
confused. What is the relationship between
the pH and KH buffer? It sounds like both
buffer capabilities referring to the same
thing. We find it helpful to think of the
KH buffer as a sub-set of pH buffer. This
is because it is possible that your pH level
is low and the KH level is high at the same
time. The other contributing factor in the
case of a decrease of pH level is the level
of Calcium (Ca) ions. So there are two factors
that contribute to the pH buffer capability
in general: KH buffer and level of Calcium
ions.
Maintaining your KH level
The KH-test is to measure the concentration
of the carbonate and hydrogen carbonate ions
in the water sample. Most KH-test kits include
chemical solution for you to dip into the
water sample. Count the number of droplets
needed to turn the color of the water sample.
Then calculate the concentration according
to the instructions included in the test
kit.
To maintain your KH-buffer capability means
to add carbonate ions to replace the ones
that were used up in previous neutralizations.
One way of doing this is to add Calcium Carbonate
(CaCO3). However, adding calcium carbonate directly
has only a limited result. Calcium carbonate
does not dissolve into the water quickly.
It has been found that the dissolving process
can be speeded up by passing carbon dioxide
gas through solid calcium carbonate.
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Technology Section
Now that you have appreciated a stable pH
level and the the importance of the pH and
KH buffer capability, let us introduce the
following system to handle all of the issues
simultaneously for you. The system has a
pH controller, a Calcium reactor, and a CO2 regulator.
To measure the pH level accurately, we recommend
the use of a pH meter. However, a better
option is the use of a pH controller. A pH meter can at most indicates the pH level
in your tank. But a pH controller can automatically
adjust the pH level of the water if the pH
level drops below the lower limit pre-determined
by you.
Above are two pictures of the same pH controller.
The pH controller (on the right-hand-side)
is an Aqua Medic product (on the left-hand-side).
Click on the Calcium Reactor to see another
picture of the gravel in the middle section
of the tower. (New)
The Calcium Reactor and the Carbon Dioxide
Regulator
The calcium reactor is a stand-alone unit
that takes water branched out from the main
pump of your system. It has a recycle pump
on the top of the tower that is responsible
for the water circulation inside the tower.
The reactor also has an inlet for the carbon
dioxide regulator. As the water is being
circulated, carbon dioxide gas from the regulator
is being dissolved into the water. The saltwater
with the carbon dioxide gas dissolved is
then passed through the calcium carbonate
gravel layer (the middle section of the calcium
reactor shown above). The presence of the
carbon dioxide molecules in the water can
help the carbonate molecules in dissolving
into the water quickly. The outlet has a stream of calcium carbonate
mixture of 450 mg/l that is ready to be circulated
back to the tank. The mixture, however, also
has a certain amount of carbon dioxide molecules
that did not chemically react with the calcium
carbonate gravel.
The pH Controller and the Carbon Dioxide
Regulator
The pH controller which is connected to the
carbon dioxide regulator has a probe sitting
inside the reactor to sense the pH level
of the aqueous mixture. The pH controller
can be programmed to sense the pH at a particular
level. We recommend you to set the pH level
to 6.5. The probe constantly monitors the
pH level. Once the pH level is below 6.5,
it signals the solenoid in the carbon dioxide
regulator to shut off the valve.
Why shut off the regulator? Remember from
the above discussion of photosynthesis that
the addition of carbon dioxide decreases
the pH level in the water. So stopping any
further release of the carbon dioxide gas
allows the tank itself to kill off the excess
carbon dioxide produced by the regulator.
Since the calcium reactor should be used
with the carbon dioxide regulator and the
pH controller can take care of the excess
carbon dioxide automatically, we highly recommend that you use this entire
set of equipment so that you can have all
the associated problems handled immediately.
Note:
We have all of these three products: pH controller,
Calcium reactor, and Carbon Dioxide Regulator
available in stock. Please contact us if
you are interested in the system described
above.
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