(I hope this formates correctly, it may take a few tries...) (addendum, the boxes in the equations are "yields" arrows, they are representing equilibria, and usually indicate reactions in BOTH directions)
Hey MM,
I’ll try and address each point here, and give you a little background on Ca++ in the marine Microcosm.
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Do you know if calcium chloride is what makes up the majority of the above mentioned calcium supplements. b/c I belive kalk is calcium hydroxide
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Depending on whether the source or intent of the product is to correct Ca++ only or to correct Ca++ AND alkalinity. Most products that contain only CaCl2 will only push up Calcium levels, and then only for a short period of time. In addition, most of our need for calcium would be in somewhat alkaline (pH of 8.0 to 8.4) ranges, and we try to avoid additions of substances that produce acids or use up alkalinity. CaCl2 in the presence of water dissociates into Calcium oxide and hydrochloric acid, NOT GOOD!:
CaCl2 + 2 H2O Ca(OH)2 + 2 HCl and Ca(OH)2 CaO and H2O
Calcium is very insoluble in seawater (heh, look at it in terms of it’s levels, …ppm!!!!) and administering it to the seawater levels we have in quantities of more than 400 or so ppm will end up with precipitation of that excess (buffer systems allow us to exceed this absolute limit through supersaturation of systems). Factors that affect the solubility of calcium in seawater mostly depend on the anion associated with the solute, the temperature of the aqueous phase, and the pH and buffering capacity of that solution. Calcium for the most part has a positive temperature coefficient of solubility, that is, as temperature increases in the solution, calcium becomes more soluble (want more info? Check out Le Chatelier’s principle) However, this becomes much more complex as the temp rises over around 85 F, as there is a degassing of CO2 from solution, more on this later. Pressure affects solubility, but because liquids and solids are, for all purposes in the aquaria, incompressible, it has little affect on Ca++ concentrations, although it does affect CO2 levels in seawater. When thinking of CaCO3, the equilibrium that is established by the dissociation into CaO and CO2 can be drastically affected by the removal or addition of CO2 to the solution by animal respiration or other biological processes (i.e. plant processes in the absence of sunlight…) including barometric changes in the atmosphere. When CO2 levels go up in seawater, we see:
CaCO3 + CO2 + H2O Ca(HCO3)2
AND
CaCO3 + H2O Ca(OH)2 + H2CO3
Which increases the solubility of Calcium by forming another anion/cation pair (a new AND separate equilibrium equation) with Bicarbonate, which is much more soluble than CaCO3 alone. This also leads to the increases in buffering capacity/alkalinity that we desire for our aquaria. By increasing the concentrations/availability of the Bicarbonate ion, we increase that alkalinity factor so desired by out little critters. We now have (starting with CaCO3 or Ca(OH)2 instead of CaCl2:
CO2 + H2O -- H2CO3 - HCO3- + H+
And
Ca(HCO3)2 - Ca++ + 2 (HCO3--)
And
Ca(OH)2 + 2CO2 - CaCO3 + H2O
All in dynamic equilibrium (and now giving buffer capacity and calcium):
CO2 + H2O H2CO3(carbonic acid) (H+) + HCO3- (Bicarbonate)
(H+) + HCO3- (Bicarbonate) + Ca(OH)2 2 H2O + CaCO3 !!!
This is the basis of the carbonate/bicarbonate buffer system in seawater. Additions of CaCO3 on the left end (by adding Calcium as the carbonate) or through the use of Kalkwasser ( Ca(OH)2 or CaO ) will not only improve calcium levels, but will improve the alkalinity/buffer capacity of our water column. The solubility or rather, the INSOLUBILITY of Calcium Carbonate is a possible sink (source of removal) for calcium from this dynamic equilibrium. Calcium ion is also removed by biological action (skeletal deposition by
stony corals) and by significant levels of phosphate, which is much more insoluble than Carbonate, to form both dibasic and tribasic calcium Phosphate (if you want to see the chemistry, you’ll have to email me on this one, a little more complicated than I want to type and format for this thread). In addition, biological processes that produce organic acids (DOM decomposition, etc) will reduce the amounts of bicarbonate, as well and increases in dissolved carbon dioxide (leading to the formation of carbonic acid and a proton). To answer your question, Most of the USEFUL additives are either CaCO3 or Ca(OH)2/CaO.
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Are the test kits we use geared to test chloride CaC03 or hydroxide CaCo3 or both b/c calcium is calcium using any drop and count test kit?
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Almost all the test kits for the marine (note I SAID SALTWATER) aquaria test for calcium as the cation (dissociated calcium ion). Although you could add 500 GMS of calcium carbonate to a liter of water, the test kits will only show the amount of calcium that has dissolved and is in solution (i.e., for pH of 7.0, around 350 to 400 PPM). The other 499.999650 GMS of the calcium Carbonate will be on the bottom of the flask as undissociated CaCO3 and will not be measurable.
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… if I haven't rambled enough yet at 2:00 in the morning I think the coffee is kicking in
Does Bio available calcium or chelating agent in solution what we add when we simple add our trace elements, is this the only way to achieve this or is the consumption of precipitated calcium unattainable?
Is there a chelated calcium kit or conversion formula for this reading?
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I think that any organism can consume the precipitated calcium, either by eating the precipitate out of the sand bed, or mistaking a precipitated flake as food, but for the most part this is insignificant. Antacids like TUMs are calcium carbonate. We can absorb Ca++ from them because our digestive tract uses large quantities of HCl to solubilize the calcium as carbonate, but even so, there is a large amount of Calcium carbonate that is not available through oral digestion/absorption. For most creatures (I can’t really think of any that do otherwise), the utilization of calcium for either bone or other skeletal use requires that it be in the ionic form.. Chelation of a substance, by definition, is putting it in a form with a large molecule that prevents it from exerting its normal behavior in a biological or chemical sense. The term “chelate” is used to define a large molecule that results form the combination of an electron donor with a metal. The compounds capable of acting as an electron donor for the metals are called ligands. Chelates must follow this definition, otherwise if they form actual bonds; they are termed either organometalic compounds or metal complexes and do not react in the same way as chelates. The normal reactions of a metal disappear when a chelate is formed. The chelate may serve to prevent precipitation of the ion when it would normally do so otherwise. In biological systems, Nature uses chelation to do things with metals that would not be possible otherwise, for example, amino acids, proteins, and tricarboxylic acid molecules are used in vertebrates as ligands for zinc, copper, iron, cobalt, and manganese to make these substances biologically available (their reactivity would preclude this otherwise). Hemoglobin is a vertebrate example with iron, Magnesium in Chlorophyll, copper in various oxidases and peroxidases for the citric acid cycle, zinc in Insulin, and cobalt in cyanocobalamin (Vit b-12). The availability of the metal in a metal-ligand combination is dependant on the strength of the ionic bond that is formed, but suffice it to say that unless the test kit has some way of dissolving the bond for Calcium so that is can be dissociated from the ligand, there would be little way to measure the level of chelated Calcium in most biological or aquarium systems (unless the test kit were able to detect the ligand, then a direct quantitation could be extrapolated for the amount of Calcium associated with the ligand).
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These are the que's that keep me up at night morning ya know what I mean it's sad I know
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Me??? I never stay up late!!! (Yeah, I can hear Alice and Dick and Doug laughing now…)
I know this is kind of deep, but a good understanding of these systems will make it much easier3 to make legitimate decisions about how you will manipulate these systems.
Hope this helps.
Tom (Reefaroni)
[This message has been edited by tdwyatt (edited 02-03-2001).]
am I on the road to ruin using B-ionic till I get a 
snivle snivle tear tear.
