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Understanding Calcium and
Alkalinity Understanding water chemistry can be one of
the most frustrating aspects to new or seasoned aquarists alike without
a formal education on calcium and alkalinity and how they can affect
each other. Most hobbyists do not like to read scientific writings
about water chemistry or look at scientific equations ([SiO(OH)3−]
+ H+ → [Si(OH)40])
depicting such and not understand what they are even looking at or
reading about. Orphek will attempt to simplify marine water
chemistry in this article. Stable and consistent levels of calcium and
alkalinity not only insure growth of calcareous invertebrates, but also
are required for their survival in both the ocean and our captive
systems. Coral, coralline algae, and animals with shells are made up of
more than just calcium; they also contain carbonates which are called
buffers. Buffers contain calcium carbonate, borate, and bicarbonate.
Without these buffers or carbonates, corals cannot lay down their
calcium skeletons which make up the massive coral reefs found in our
oceans. Corals absorb bicarbonate and process it into carbonate in
order to build their calcium carbonate skeletons. Proper lighting
of the correct intensity and spectral range is also required.
Magnesium also plays a role in calcification, without its presence
corals cannot absorb the calcium in the levels that are available to
them. Magnesium levels are three times higher than calcium levels
in natural seawater and should also be maintained in that ratio in our
captive reef systems. Calcium (Ca) level of 400-450ppm and a
magnesium (Mg) level of 1200-1350ppm are recommended for mature corals.
For faster growth of frags and juvenile corals, Orphek recommends a
calcium level of 465ppm, Mg at 1390ppm, and dKH at 12.6. The higher dKH
provides additional carbonates to increase growth rate and the higher
calcium level compensates for increased calcium absorption by the
corals. Mg is increased to adjust for the recommended three to one
ratio of calcium and magnesium. These increases balance out the water
chemistry and they are not raised to a level which would cause
precipitation. dKH (Degree of Carbonate Hardness) is not a
thing in the water nor is it an element. It is a measure of
whether adequate carbonates are present in the water to ensure continued
coral growth and to keep the pH stable. Carbonates increase
alkalinity levels much more than bicarbonates and well designed buffers
should contain about 85% carbonates to maintain a pH of 8.0. In
natural seawater, alkalinity varies between 6.2 to 8.2dKH (depending on
location) and is maintained by the occurrence and dissolution of
carbonate rocks/coral skeletons and carbon dioxide in the atmosphere.
The presence of carbon dioxide in seawater helps to slowly dissolve
carbonates and this is why CO2 is used in calcium reactors. Now that we have a good idea of how these
elements interact with each other in nature, we will move on to how
these elements can change and effect other elements and parameters in
our home systems. The ideal pH for our reef systems is 8-8.2.
In the ocean this is easily maintained due to the enormous surface area
which exchanges CO2 for oxygen, and the fact that very little dissolved
nutrients are present which can acidify the water. In our captive
reef systems this can be challenging, especially if we overstock our
systems without proper filtration, air exchange, nutrient export, water
flow, and adequate alkalinity to keep pH levels at a desirable level.
Protein skimmers are highly recommended and should be selected at a
capacity rated twice the size of your reef aquarium. This will
ensure efficient nutrient export which will minimize buffer dosing.
The two factors which lower pH are excessive nutrients and carbon
dioxide and both of these are generated from excessive animal stocking
which leads to more animal waste and carbon dioxide. Fish expel
carbon dioxide with every breath they take and this can be minimized by
using the largest sump your space will accommodate. This provides
a larger surface area to ensure good gas exchange and oxygen uptake.
A good flow rate in the aquarium is also necessary so water is
constantly moving and being drawn into the sump where CO2 can be
exported and oxygen imported into the system. It is not unusual
for pH levels to drop by as much as three units (0.3) in the evening
because photosynthesis, which utilizes carbon dioxide, does not occur
which in turn can lower pH. Good flow rates also keep detritus and
uneaten food in suspension where they can be exported into the sump
where scavengers can feast on them and/or the protein skimmer can export
them out of the system before developing into dissolved nutrients.
A non laminar flow is highly desirable and the use of programmable pumps
such as the Ecotech Vortex MP models easily provides this. The use
of this pump technology ensures good water movement in all areas of the
aquarium and is more natural for a coral environment. A total flow rate
of at least 12 times the aquarium volume is highly recommended. The dKH of a reef system should be kept at 7
to 8.5. Levels above this are not necessary in a well maintained
system and are undesirable as it can lead to calcium precipitation
unless balance between dKH and calcium is carefully monitored.
Acids commonly known to lower dKH levels are CO or carbon dioxide,
nitric acids and organic acids, the latter two being derived from sand
beds containing large amounts of detritus and from uneaten foods and
waste which turn into dissolved nutrients which lead to higher than
acceptable nitrate levels. Some aquarists with heavily stocked
aquariums will provide a means of carbon dosing in an attempt to lower
nitrate levels. This process basically involves feeding nutrient
eating bacteria with a carbon source which causes them to multiply in
large numbers which in turn consume more dissolved nutrients thereby
reducing acids in the water. These nutrient rich bacteria slough
off and become suspended in the water column and provide a good food
source that are readily consumed by corals and other filter feeding
invertebrates. A word about calcium precipitation is necessary here and we
will try to explain this in a clear manner. Many aquarists tend to
keep dKH levels higher than necessary thinking more is better.
This is not the case with buffers (carbonates). It is only
possible to dissolve a given number of solids in a given amount of
seawater, and these include calcium, carbonates, and most every element
found in seawater. For a simple analogy we will use poker chips to
explain. If we have a hundred poker chips that completely fill a
bowl and seventy of these chips are red to represent calcium, and thirty
of these chips are green to represent carbonates or buffers
(alkalinity), in theory our bowl is filled and we cannot add any more.
If we rapidly increase the red chips (calcium), some of the green chips
(alkalinity) would have to be removed. So by dosing excess amounts
of calcium (red chips), we precipitate the carbonates (green chips) out
of solution thereby causing what is known as the “snowstorm” effect.
Many aquarists that see this effect immediately begin to dose other
elements in an attempt to balance this out. This is foolish and
will not work, it will only feed the effect by trying to add more chips
in an already over filled bowl which can lead to increased
precipitation. This event will have to run its course and only
then can you slowly establish a calcium/alkalinity balance within the
aquarium. Calcium carbonate precipitation can be even more drastic
at higher pH levels that can occur if Kalkwasser is used and is not
slowly dosed. As the pH rises, the amount of calcium and
alkalinity that can be kept in solution without precipitation decreases.
High pH levels will convert much of the bicarbonates present into
carbonates which lead to carbonate spikes which again produce the
snowstorm effect. This is why you see residual on the bottom of a
Kalkwasser mixing vessel, it cannot go into solution due to an excess of
carbonates. Keeping your water chemistry balanced by
regularly testing for pH, calcium, alkalinity, and magnesium will assure
continued health for your reef inhabitants. If you need to raise
or lower calcium or alkalinity, do it slowly and do one at a time, not
both on the same day. Orphek hopes this will simplify your
understanding of how calcium and alkalinity can react with each other.
Orphek doesn’t just produce high PAR/PUR LED lighting for your corals,
we extensively study corals and their reactions to both lighting and
water chemistry. Not only do we produce the best lighting for your
corals, we want your corals to grow and thrive and provide this
information to you, the aquarist, our highly regarded asset. This article is provided by James Gasta
(sales-3@orphek.com ) who is
employed by Orphek LED and generates blogs and articles for the Orphek
website, www.orphek.com .
James also volunteers his time as a crew member for wet web media
(crew@wetwebmedia.com ). |
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