mmkeeper
Well-known member
Just a question. What is the benefit to using Kalw as top off water with a calcium reactor?
Using Kalw w/calcium reactor
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reedman
Well-known member
Kalk will help to stabilize the natural swings in PH if used on a timer or dripped at night when the PH drops. It also offsets some of the low PH of the effluent of the Ca Rx.
DonW
R.I.P.
Travis_s said:
Help me understand that one.
Don
DonW
R.I.P.
Travis_s said:
Are you assuming that because co2 causes kalk to precip that the co2 becomes unavailible to algae??
Don
No, Limewater "uses" CO2 in the saltwater and the hydroxide ions from the limewater to form alkalinity... so after the limewater inters the tank, the amount of CO2 is reduced. This makes it so some of the CO2 (whatever the limewater uses up) is unavailable for use by algae.
I think this can explain it better than I... http://web.archive.org/web/20010421...brary/articleview2.asp?Section=&RecordNo=2074
tdwyatt
Member
at the local pH of the microenvironment created by the kalk (high pH due to concentration of (OH-) ion from Ca(OH)2). the hydroxyl ion reacts with the dissolved CO2 as carbonic acid
Carbonic acid is a carbon-containing acid with the formula H2CO3, the name usually associated with solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates (or hydrogencarbonates) and carbonates, and in ASW or NSW are responsible for the establishment of the bicarbonate/carbonate buffer system.
Carbon dioxide dissolved in water is in equilibrium with carbonic acid:
CO2 + H2O <---> H2CO3
The equilibrium constant at 25°C is 1.70×10^−3: hence, the majority of the carbon dioxide is not converted into carbonic acid and stays as CO2 molecules. In the absence of a catalyst, the equilibrium is reached quite slowly, with forward rate constants at 0.039 s^−1 for the forward reaction
CO2 + H2O ---> H2CO3
...and 23 s^−1 for the reverse reaction
H2CO3 → CO2 + H2O
The equilibrium between carbon dioxide and carbonic acid is very important for controlling the rate of change for the pH of the SW water column. Corals use an enzyme, carbonic anhydrase at the calcioblastic endothelium which catalyzes the conversion between the two compounds, increasing the reaction rate by a factor of nearly 109.
Carbonic acid has two acidic hydrogens and so two dissociation constants:
***Care must be taken when quoting and using this first dissociation constant of carbonic acid. The value quoted above is correct for the H2CO3 molecule, and shows that it is a stronger acid than acetic acid or formic acid: this might be expected from the influence of the electronegative oxygen substituent. However, carbonic acid only ever exists in solution in equilibrium with carbon dioxide, and so the concentration of H2CO3 is much lower than the concentration of CO2, reducing the measured acidity. The equation may be rewritten as follows (c.f. sulfurous acid):
CO2 + H2O <---> HCO3− + H+
Ka = 4.30×10−7 mol/L; pKa = 6.36.
This figure is often quoted as the dissociation constant of carbonic acid, although this is somewhat ambiguous, it might better be referred to as the acidity constant of carbon dioxide, as it is particularly useful for calculating the pH of CO2 solutions. For our purposes here, this is useful in establishing how reactive the ionic specie will be with the hydroxyl, and the rate constant will determine how quickly the bicarbonate/carbonate system can develop in seawater, as it is the far left end of this equilibrium. It is the reason we see kalkwasser develope increased buffering due to the presence of the hydroxyl ion
It is usually not possible to obtain pure hydrogen bicarbonate as the presence of even a single molecule of water causes the carbonic acid to revert to carbon dioxide and water fairly quickly. However, pure carbonic acid has been found to be quite stable in the absence of water, with a calculated half-life of 180,000 years. There is a hypothetical acid orthocarbonic acid which is even more hydrated, being H4CO4.
However, the slow conversion of Carbonic acid to hydrocarbonate is enhanced at higher pH due to the pKa of this compound, so that the microenvironment of a kalkwasser drop provides the ideal environment for the formation of calcium hydrocarbonate, allowing for an initial supersaturation, followed by rapid dissolution as the ions in this mix are quiuckly diluted down to the system's values for these substances. This is the main reason to slowly drip kalk into your system into rapidly moving areas of water. The concentration of kalk-sourced hydroxyl in relation to most systems' CO2 content is such that the delivery rate of calcium and hydroxyl ions is easily matched by the ability of CO2 to rapidly dissolve from the atmosphere into the water column to replace the utilized supply of CO2 for this reaction. So long as the atmosphere above the aquarium has good circulation with the open atmosphere, and there is good surface turbulance for the surface, CO2 supply will not be a limiting factor in the production of in-tank alkalinity by a kalk drip. This is especially true in systems with excess dissolved CO2 from improperly adjusted Ca reactors.
HTH clarify the issue.
Carbonic acid is a carbon-containing acid with the formula H2CO3, the name usually associated with solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates (or hydrogencarbonates) and carbonates, and in ASW or NSW are responsible for the establishment of the bicarbonate/carbonate buffer system.
Carbon dioxide dissolved in water is in equilibrium with carbonic acid:
CO2 + H2O <---> H2CO3
The equilibrium constant at 25°C is 1.70×10^−3: hence, the majority of the carbon dioxide is not converted into carbonic acid and stays as CO2 molecules. In the absence of a catalyst, the equilibrium is reached quite slowly, with forward rate constants at 0.039 s^−1 for the forward reaction
CO2 + H2O ---> H2CO3
...and 23 s^−1 for the reverse reaction
H2CO3 → CO2 + H2O
The equilibrium between carbon dioxide and carbonic acid is very important for controlling the rate of change for the pH of the SW water column. Corals use an enzyme, carbonic anhydrase at the calcioblastic endothelium which catalyzes the conversion between the two compounds, increasing the reaction rate by a factor of nearly 109.
Carbonic acid has two acidic hydrogens and so two dissociation constants:
H2CO3 --->HCO3− + H+
Ka1 = 2.5×10−4 mol/L
pKa1 = 3.60. ***
HCO3− --> CO32− + H+
Ka2 = 5.61×10−11 mol/L
pKa2 = 10.25.
Ka1 = 2.5×10−4 mol/L
pKa1 = 3.60. ***
HCO3− --> CO32− + H+
Ka2 = 5.61×10−11 mol/L
pKa2 = 10.25.
***Care must be taken when quoting and using this first dissociation constant of carbonic acid. The value quoted above is correct for the H2CO3 molecule, and shows that it is a stronger acid than acetic acid or formic acid: this might be expected from the influence of the electronegative oxygen substituent. However, carbonic acid only ever exists in solution in equilibrium with carbon dioxide, and so the concentration of H2CO3 is much lower than the concentration of CO2, reducing the measured acidity. The equation may be rewritten as follows (c.f. sulfurous acid):
CO2 + H2O <---> HCO3− + H+
Ka = 4.30×10−7 mol/L; pKa = 6.36.
This figure is often quoted as the dissociation constant of carbonic acid, although this is somewhat ambiguous, it might better be referred to as the acidity constant of carbon dioxide, as it is particularly useful for calculating the pH of CO2 solutions. For our purposes here, this is useful in establishing how reactive the ionic specie will be with the hydroxyl, and the rate constant will determine how quickly the bicarbonate/carbonate system can develop in seawater, as it is the far left end of this equilibrium. It is the reason we see kalkwasser develope increased buffering due to the presence of the hydroxyl ion
It is usually not possible to obtain pure hydrogen bicarbonate as the presence of even a single molecule of water causes the carbonic acid to revert to carbon dioxide and water fairly quickly. However, pure carbonic acid has been found to be quite stable in the absence of water, with a calculated half-life of 180,000 years. There is a hypothetical acid orthocarbonic acid which is even more hydrated, being H4CO4.
However, the slow conversion of Carbonic acid to hydrocarbonate is enhanced at higher pH due to the pKa of this compound, so that the microenvironment of a kalkwasser drop provides the ideal environment for the formation of calcium hydrocarbonate, allowing for an initial supersaturation, followed by rapid dissolution as the ions in this mix are quiuckly diluted down to the system's values for these substances. This is the main reason to slowly drip kalk into your system into rapidly moving areas of water. The concentration of kalk-sourced hydroxyl in relation to most systems' CO2 content is such that the delivery rate of calcium and hydroxyl ions is easily matched by the ability of CO2 to rapidly dissolve from the atmosphere into the water column to replace the utilized supply of CO2 for this reaction. So long as the atmosphere above the aquarium has good circulation with the open atmosphere, and there is good surface turbulance for the surface, CO2 supply will not be a limiting factor in the production of in-tank alkalinity by a kalk drip. This is especially true in systems with excess dissolved CO2 from improperly adjusted Ca reactors.
HTH clarify the issue.
tdwyatt
Member
mojoreef said:
I have to come over and post at least once a year...
Using kalkwasser and CO2 reactors won't hurt, as if there is an excess of CO2 in the water column, it will fix the issue and supply extra Calcium snd Alkalinity as a bonus, but this is usually an unnecessary fix if you have a Ca reactor appropriately sized for the system in question (and it is properly adjusted/controlled). This usualy means using a pH controller with the solenoid from the regulator plugged into the low pH outlet and the probe frm the controller placed in the effluent line from the primarly column. In this manner, and with the pH controller set to keep the pH between 6.65 and 6.75, you'll get maximal dissolution of the aragonite with little waste of CO2 (and you won't turn the medium into mush). Especially with a second column, using this method will keep your tank pH between 8.15 and 8.25 (measure with a second pH meter locted upstream from the effluent dischsarge point for the Ca reactor) while still keeping your Ca++ and alk (HCO3-) in the Ca=400-425PPM+ and HCO3=10-12 dKH ranges, even with heavy hermatypic coral pops in the tank. I am sure that with a mismatch of reactor size to tank size that the Ca/Alk supply can be outstripped by the system's population, but in a stony tank in the 250 G (US) size and down, this would be difficult to do if the reactor were correctly tweaked with the controller and CO2 supply.
Now if it were that monster "L" tank...
The site looks great, you've been busy!
tdwyatt
Member
Heh! I may have mised your actual question.
Yes, the use of a Kalk reactor will remove the excess CO2 that might otherwise be available to algae for growth, but the conversion into alkalinity in a marine system accounts for the whereabouts for most of the CO2 anyway, so that accurate and appropriate adjustments of your CO2 delivery rate will reduce overall CO2 delivery to the water column, AND since the rate for the kinetics of the reaction for carbonic acid to CO2 is so much faster than the forward rate of the reaction (see the post above), the majority of the carbon dioxide is not converted into carbonic acid and stays as CO2 molecules, which is easily degassed from the water column as turbulence and gas exchange occurs in the system. The only systems that should experience problems are those with chronically very low pH readings (i.e., "tight" tanks with tight-fitting lids or glass covers, or systems located in "tight" homes where there is an accumulation of CO2 in the indoor environment).
Not really sure whether or not I answered you question, Mike, right now I am addressing an uptake issue on which does a better job of absorbing/uptaking nutrients, microalgae or macroalgae over in The Think Tank at TRT, but you name came up in a discussion with one of my Logansville buddies, so I though I'd better make sure you had not fallen off the face of the earth (as Alice evidently has)
Yes, the use of a Kalk reactor will remove the excess CO2 that might otherwise be available to algae for growth, but the conversion into alkalinity in a marine system accounts for the whereabouts for most of the CO2 anyway, so that accurate and appropriate adjustments of your CO2 delivery rate will reduce overall CO2 delivery to the water column, AND since the rate for the kinetics of the reaction for carbonic acid to CO2 is so much faster than the forward rate of the reaction (see the post above), the majority of the carbon dioxide is not converted into carbonic acid and stays as CO2 molecules, which is easily degassed from the water column as turbulence and gas exchange occurs in the system. The only systems that should experience problems are those with chronically very low pH readings (i.e., "tight" tanks with tight-fitting lids or glass covers, or systems located in "tight" homes where there is an accumulation of CO2 in the indoor environment).
Not really sure whether or not I answered you question, Mike, right now I am addressing an uptake issue on which does a better job of absorbing/uptaking nutrients, microalgae or macroalgae over in The Think Tank at TRT, but you name came up in a discussion with one of my Logansville buddies, so I though I'd better make sure you had not fallen off the face of the earth (as Alice evidently has)
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