New idea for calcium
- Thread starter Foxy Brown
- Start date
The endpoint for a proper alkalinity titration for ocean water is 4.2. The indicator dyes are irrelevant to what the endpoint <b>should</b> be, and they're not even needed. It's possible to titrate with a pH meter if it's accurate in the relevant range.
If you dose the vinegar (which I think you plan to use for your acid) at a very slow rate, I agree that you won't see much fizzing, but I don't think you'll be able to add very much calcium or alkalinity, either. It'll be interesting to see your results.
If you dose the vinegar (which I think you plan to use for your acid) at a very slow rate, I agree that you won't see much fizzing, but I don't think you'll be able to add very much calcium or alkalinity, either. It'll be interesting to see your results.
Foxy Brown
New member
I agree with you in principal. I think the standard indicator is methyl orange which is pH = 4.6 if memory serves... again it's been over a decade since I looked at this carefully. (Maybe it shifts to 4.2 in saltwater?) I believe the reason to use this pH is to make sure the bicarbonate is completely reacted.
pH = 6.37 + log (HCO3-/ H2CO3) so at pH = 4.6, this gives about 98% conversion of bicarb to carbonic acid.
Of course, this is about midway through the acetate reaction, so it will change the result of the titration, and give apparently higher alklinity. But the point we want to know if not really how many moles of acid it takes to reach a pH at which all your tank's inhabitants are dead anyway. The real question is: "What is the bicarbonate concentration?". This is why I have long been a proponent of using direct measurement of ion concentrations like w/ an ISE rather than by titration.
Acetate serves no purpose in calcification process (AFAIK) and serves no purpose in buffering pH in this range, so it serves no real purpose at all except in adding DOC. So, while adding acetate will change the result of an alkalinity test, it's not doing anything to help calcification for corals, clams, etc. For this reason, i think discussion should ignore the effects of acetate on alkalinity, except to keep in mind it might throw-off an alkalinity test. Sooner or later it will be converted to carbonate, and this is really what we want.
The point of adding dissolved CO2 not effecting alkalinity is 100% true, but totally beside the point. The concentration of CO2 in equilibrium w/ carbonate is essentially zero. The reactor design is purposefully meant to allow everything to come to equilibrium. Thus, we never add CO2 to to the tank, only acetate and bicarbonate. The relative amount of these - 1:1 or less, depend on assumptions about anoxic bacterial metabolism which have no real basis. In DI water, the solubility of O2 is a few ppm. We are talking about acetate concentrations of several thousand ppm. Since there is no alternate terminal electron acceptor, I do not believe bacterial metabolism to be of any real concern, and in any event its only outcome would be a slight increase in bicarb concentration which is not a problem.
Thus, I would expect such a reactor to output 1 mole of Ca2+, 1 mole of H3CCOO- and 1 mole of HCO3 for each mole of acetic acid added. Thus for each 1mL of 5% vinegar dosed per liter of tank water, we add 32ppm of Ca, 49 ppm of actual bicarbonate, and perhaps ~4 dKH of alkalinity on a test.
Sorry for the chem speak.
Foxy Brown
New member
Our good friend Randy Holmes-Farley published and article in advanced aquarist describing the problem of acetate as an interference in alkalinity testing and he proposed a modified titration procedure which ignores acetate.
http://www.advancedaquarist.com/2002/2/chemistry
So this gives me a little backup in saying that acetate is not real alkalinity but an artifact (interference) in the alkalinity test.
http://www.advancedaquarist.com/2002/2/chemistry
So this gives me a little backup in saying that acetate is not real alkalinity but an artifact (interference) in the alkalinity test.
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disc1
-RT * ln(k)
You keep talking about how this acetate will be metabolized into CO2. Write out a balanced equation for that. See the waters? Where are the 3 other protons coming from? Now you see why I say you're adding alkalinity?
It doesn't matter if you're talking about carbonate directly or not, equivalents of alkalinity are equivalents of alkalinity. They don't just appear and disappear. It all has to balance in the end.
Foxy Brown
New member
An easy way to balance acetate metabolism is:
CH3COO- + 4O2 -> 2CO2 + H2O + OH-
Now whether this is the RIGHT way to balance it or not, I can't say. Real biological processes involve protons moving around all over the place. I don't claim to be a biologist.
However, there is a difference between ions, just because the ion carries a minus charge does not make it alkalinity. The pKa of the acid is very important, so a chemical change from 1 anion to another does not mean alkalinity is conserved. I stand by the fact that acetate is not real alk.
Now the equation I wrote gives off OH- which does count toward alkalinity, and the CO2 is neutral in those terms. As such, in the end acetate may indeed give alk... after metabolism. But I'm not qualified to judge since I don't understand the reaction pathway - I just think it doesn't count on its own.
In any event, it's a sideshow. That just mean we get balanced Ca and Alk out of the reactor one way or another, which is a fine thing and more justification for it as a new way of dosing Ca.
CH3COO- + 4O2 -> 2CO2 + H2O + OH-
Now whether this is the RIGHT way to balance it or not, I can't say. Real biological processes involve protons moving around all over the place. I don't claim to be a biologist.
However, there is a difference between ions, just because the ion carries a minus charge does not make it alkalinity. The pKa of the acid is very important, so a chemical change from 1 anion to another does not mean alkalinity is conserved. I stand by the fact that acetate is not real alk.
Now the equation I wrote gives off OH- which does count toward alkalinity, and the CO2 is neutral in those terms. As such, in the end acetate may indeed give alk... after metabolism. But I'm not qualified to judge since I don't understand the reaction pathway - I just think it doesn't count on its own.
In any event, it's a sideshow. That just mean we get balanced Ca and Alk out of the reactor one way or another, which is a fine thing and more justification for it as a new way of dosing Ca.
Foxy Brown
New member
I'll give and example of why alk is not necessarily conserved...
If I try to balance oxidation of acetate w/ nitrate (anaerobic metabolism) I get:
8NO3- + 5CH3COO- -> 4N2 + 10CO2 + H2O 13OH-
FYI, this was my work, but matches the earlier post by kenny b.
It has to be written this way since neither anion should protonated at pH = 8.x and you must conserve charge... Since nitrate definitely doesn't count toward alk, we have an enormous increase in both pH and alk overall likely, this will wind up with CO2 + OH- -> HCO3-, so more alk that pH increase in reality. The point is I'm in no way sure this is a realistic reaction pathway as it seems a bit odd, but it is balanced and does not conserve alk.
Since I'm not sure of these reactions, nor how much is going on in aerobically vs anaerobically it's difficult to predict what is actually happening. I prefer not to assume I can predict the biological processes
If I try to balance oxidation of acetate w/ nitrate (anaerobic metabolism) I get:
8NO3- + 5CH3COO- -> 4N2 + 10CO2 + H2O 13OH-
FYI, this was my work, but matches the earlier post by kenny b.
It has to be written this way since neither anion should protonated at pH = 8.x and you must conserve charge... Since nitrate definitely doesn't count toward alk, we have an enormous increase in both pH and alk overall likely, this will wind up with CO2 + OH- -> HCO3-, so more alk that pH increase in reality. The point is I'm in no way sure this is a realistic reaction pathway as it seems a bit odd, but it is balanced and does not conserve alk.
Since I'm not sure of these reactions, nor how much is going on in aerobically vs anaerobically it's difficult to predict what is actually happening. I prefer not to assume I can predict the biological processes
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Foxy Brown
New member
BTW, I balanced those myself and didn't use kenny b's numbers so at least I confirm his result.
disc1
-RT * ln(k)
You sure that's balanced? Count your oxygens.
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Foxy Brown
New member
Quite right.
I agree that corals can't use acetate for building their skeletons, and true dKH (carbonate hardness, which we don't measure) would be very useful. I think we also agree now that acetate adds alkalinity when it is consumed by bacteria? That's the idea behind one-parts, like Salifert's All-In-One, if it still is being sold.
Foxy Brown
New member
I think we're in agreement yes.
The remaining question is whether the above dosing of Acetate is advisable. For the record, I get ~32ppm of Ca and 40ppm of bicarb for dosing 1 ml of 5% vinegar per L of tank water (with the acetate going on to make some amount of alk later by consuming NO3 or O2). You then take the evaporation volume and Ca uptake over the same period and make sure you dose enough vinegar in that volume of top-off water to compensate for the Ca used. This gives about half of the acetate entering your tank per ppm of Ca when compared to the all-in-ones like Salifert.
I would love to hear back from people with a wide variety of tanks on what their evap and Ca-use rates are to see how viable the scheme is.
The remaining question is whether the above dosing of Acetate is advisable. For the record, I get ~32ppm of Ca and 40ppm of bicarb for dosing 1 ml of 5% vinegar per L of tank water (with the acetate going on to make some amount of alk later by consuming NO3 or O2). You then take the evaporation volume and Ca uptake over the same period and make sure you dose enough vinegar in that volume of top-off water to compensate for the Ca used. This gives about half of the acetate entering your tank per ppm of Ca when compared to the all-in-ones like Salifert.
I would love to hear back from people with a wide variety of tanks on what their evap and Ca-use rates are to see how viable the scheme is.
Hi!
I have just started a similar, but much simpler thing: instead of adding vinegar to kalkwasser or calcium reactor, I decided not to use any reactor, but simply start dosing Calcium acetate on a daily basis. I have been thinking about this for quite some time, and then decided to do some calculations a few days ago.
My calculation was simple. I have a 250l (about 65g) mixed reef tank which is heavily stocked by fish, so I have to dose vodka: about 5ml. daily. Calcium supplementation was using the Balling method, about 50ml. of each solution daily.
So, the Balling liquid #1 contains 55.5 of Calcium chloride, which means, 50ml of the solution will contain about 2.78g of calcium chloride, or about 0.76g of calcium.
Vodka is about 40% alcohol, in 5ml. there is 2ml of spirit, i.e. about 1.58g., that is, 0.82g of carbon.
Now, consider Calcium acetate monohydrate (CH3COO)2Ca*H2O, molar weight 176.18g. It consists of Calcium ion and acetate. However, when dissolved in tank water in very dilute form, acetate, or any organic matter, will be eaten up by bacteria. The corals too will consume it, to make Calcium carbonate. So, for simplicity of calculations, we can write Calcium acetate up in a simple form as CaH6C4O4. If we "subtract" from this CaCO3 that was consumed by corals, what remains is some non-existent C3H6O. What is of interest to us here, that in the remaining compound there are three atoms of carbon.
No, Calcium acetate monohydrate has 22.75% of Calcium. The remaining 3 atoms of carbon comprise 20.45% of molecule's weight. That is, if we take 3.4 g of the stuff, we'll yield 0.77g of calcium, and 0.7g of "free" carbon available to bacteria (to replace vodka).
So, for my setup, Calcium acetate can be a perfect substitute to replace both balling and vodka dosing: I only need to add 3.4g. of it daily. Calcium acetate powder is available through chemical shops, however in my city they did not have it. Instead, I purchased Calcium oxide and 70% acetic acid. I mixed up 100g of the acid with equal amount of water, then added about 40g. of Calcium oxide, stirring gently. Calcium oxide dissolved completely (the stuff becomes very hot), then I added a small excess of it, to neutralize the vinegar completely, waited until the excess Calcium hydroxide sediment settled, gently poured the resultant pink liquid into a different bottle, adding water to 300ml. Thus I obtained 300ml of liquid containing about 110g of Calcium acetate, i.e. 3.6g per 10ml. Thus, for my setup, I can dose just 10ml. of this liquid daily, replacing 50ml of each of the three balling liquids, and the 5ml. of vodka. I think, it will be much simpler to dose just one simple solution instead of four!
I decided to start slowly, and dosed just 3ml. on the first day, and 6ml. on the second. I will start dosing the full 10ml. dose tomorrow. I have not seen any negative effects so far.
Now, I think that I am using a significantly higher dose of carbon than an average aquarist. That is because, as I said, I have too many fish in my system. The ratio of Calcium to "excessive" Carbon in Calcium acetate is 1.11, and if someone doesn't want top add as much carbon to the system (which can result in bacterial boom, bacterial slime threads, cyano, and a general drop of Redox potential in the tank), a chemist friend at a Belorussian aquarium forum suggested that Calcium formiate Ca(HCOO)2
is a better substitute to Calcium acetate. The ratio of calcium to "excessive" carbon is 3.34, so 2.5g of Calcium formiate solution will add the same 0.77g of calcium to the system, but carbon addition will be a modest 0.23g - an equivalent of the amount contained in just 1.4ml. of vodka.
While Calcium acetate solubility is up to 400g/l, Calcium formiate will only dissolve 160g/l, but still the figure is quite good for practical usage. I will try to get some formic acid next week to make some Calcium formiate for my experiments. The stuff should also be available through major chemical stores and I heat that it must be very cheap - at least, in some countries they use tons of Calcium formiate to fight ice formation on the roads...
P.S. I am not a chemist, and I last studied the subject in my primary school. Chemistry guys, please point me if there are any flaws in my logic or calculations.
I have just started a similar, but much simpler thing: instead of adding vinegar to kalkwasser or calcium reactor, I decided not to use any reactor, but simply start dosing Calcium acetate on a daily basis. I have been thinking about this for quite some time, and then decided to do some calculations a few days ago.
My calculation was simple. I have a 250l (about 65g) mixed reef tank which is heavily stocked by fish, so I have to dose vodka: about 5ml. daily. Calcium supplementation was using the Balling method, about 50ml. of each solution daily.
So, the Balling liquid #1 contains 55.5 of Calcium chloride, which means, 50ml of the solution will contain about 2.78g of calcium chloride, or about 0.76g of calcium.
Vodka is about 40% alcohol, in 5ml. there is 2ml of spirit, i.e. about 1.58g., that is, 0.82g of carbon.
Now, consider Calcium acetate monohydrate (CH3COO)2Ca*H2O, molar weight 176.18g. It consists of Calcium ion and acetate. However, when dissolved in tank water in very dilute form, acetate, or any organic matter, will be eaten up by bacteria. The corals too will consume it, to make Calcium carbonate. So, for simplicity of calculations, we can write Calcium acetate up in a simple form as CaH6C4O4. If we "subtract" from this CaCO3 that was consumed by corals, what remains is some non-existent C3H6O. What is of interest to us here, that in the remaining compound there are three atoms of carbon.
No, Calcium acetate monohydrate has 22.75% of Calcium. The remaining 3 atoms of carbon comprise 20.45% of molecule's weight. That is, if we take 3.4 g of the stuff, we'll yield 0.77g of calcium, and 0.7g of "free" carbon available to bacteria (to replace vodka).
So, for my setup, Calcium acetate can be a perfect substitute to replace both balling and vodka dosing: I only need to add 3.4g. of it daily. Calcium acetate powder is available through chemical shops, however in my city they did not have it. Instead, I purchased Calcium oxide and 70% acetic acid. I mixed up 100g of the acid with equal amount of water, then added about 40g. of Calcium oxide, stirring gently. Calcium oxide dissolved completely (the stuff becomes very hot), then I added a small excess of it, to neutralize the vinegar completely, waited until the excess Calcium hydroxide sediment settled, gently poured the resultant pink liquid into a different bottle, adding water to 300ml. Thus I obtained 300ml of liquid containing about 110g of Calcium acetate, i.e. 3.6g per 10ml. Thus, for my setup, I can dose just 10ml. of this liquid daily, replacing 50ml of each of the three balling liquids, and the 5ml. of vodka. I think, it will be much simpler to dose just one simple solution instead of four!
I decided to start slowly, and dosed just 3ml. on the first day, and 6ml. on the second. I will start dosing the full 10ml. dose tomorrow. I have not seen any negative effects so far.
Now, I think that I am using a significantly higher dose of carbon than an average aquarist. That is because, as I said, I have too many fish in my system. The ratio of Calcium to "excessive" Carbon in Calcium acetate is 1.11, and if someone doesn't want top add as much carbon to the system (which can result in bacterial boom, bacterial slime threads, cyano, and a general drop of Redox potential in the tank), a chemist friend at a Belorussian aquarium forum suggested that Calcium formiate Ca(HCOO)2
is a better substitute to Calcium acetate. The ratio of calcium to "excessive" carbon is 3.34, so 2.5g of Calcium formiate solution will add the same 0.77g of calcium to the system, but carbon addition will be a modest 0.23g - an equivalent of the amount contained in just 1.4ml. of vodka.
While Calcium acetate solubility is up to 400g/l, Calcium formiate will only dissolve 160g/l, but still the figure is quite good for practical usage. I will try to get some formic acid next week to make some Calcium formiate for my experiments. The stuff should also be available through major chemical stores and I heat that it must be very cheap - at least, in some countries they use tons of Calcium formiate to fight ice formation on the roads...
P.S. I am not a chemist, and I last studied the subject in my primary school. Chemistry guys, please point me if there are any flaws in my logic or calculations.
Thank you, Jonathan.
I am afraid, Calcium acetate still contains too much carbon for most systems, and formiate, if the stuff is used as the main source of calcium, will be a much better choice for tanks not very heavily stocked with fish, or containing a volume of fast growing corals. I also notice that a drop of redox can be significant problem if we overdose the system with carbon and the use of ozone may be beneficial to compensate for it.
Re: my calculations, I am not sure about the influence of acetate dosing on KH. I assumed that corals will consume CaCO3, and only the remaining stuff will be available to bacteria. But this assumption was sort-of baseless, and I am not sure whether indeed the stuff will add calcium and KH in balance, or the organic part may be consumed differently (could either increase or decrease KH, depending on consumption/conversion scenario).
On another note, why do you want to avoid formic acid? Wikipedia lists it as "Formic acid has low toxicity (hence its use as a food additive), with an LD50 of 1.8 g/kg", mentioning its uses as a preservative and antibacterial agent in livestock feed.
I am afraid, Calcium acetate still contains too much carbon for most systems, and formiate, if the stuff is used as the main source of calcium, will be a much better choice for tanks not very heavily stocked with fish, or containing a volume of fast growing corals. I also notice that a drop of redox can be significant problem if we overdose the system with carbon and the use of ozone may be beneficial to compensate for it.
Re: my calculations, I am not sure about the influence of acetate dosing on KH. I assumed that corals will consume CaCO3, and only the remaining stuff will be available to bacteria. But this assumption was sort-of baseless, and I am not sure whether indeed the stuff will add calcium and KH in balance, or the organic part may be consumed differently (could either increase or decrease KH, depending on consumption/conversion scenario).
On another note, why do you want to avoid formic acid? Wikipedia lists it as "Formic acid has low toxicity (hence its use as a food additive), with an LD50 of 1.8 g/kg", mentioning its uses as a preservative and antibacterial agent in livestock feed.
I'm not very keen on working with substances that can damage eyes and skin. It's safe to eat in small quantities, though, as you state.
Dosing calcium acetate will add calcium and alkalinity in the ratio used by corals, so that part is safe enough. The acetate is converted into carbonate alkalinity:
http://reefkeeping.com/issues/2005-01/rhf/index.htm#6
Dosing calcium acetate will add calcium and alkalinity in the ratio used by corals, so that part is safe enough. The acetate is converted into carbonate alkalinity:
http://reefkeeping.com/issues/2005-01/rhf/index.htm#6
OK, I made about one liter of Calcium acetate solution (about 300g per liter) and one liter of Calcium formiate (about 150g per liter). I had do add some excess of CaO until it stopped dissolving, then let it stay for a couple of hours and filtered out the sediment. In both cases I got a bottle of clear, slightly pink to yellowish solution.
I am assuming that 10ml of the acetate solution or 17ml of the formiate solution would be adding about 0.78 g of calcium, which is the equivalent of about 2g of calcium carbonate. So I assume that a daily dose of the mentioned amount of either stuff to a given tank would compensate for roughly 2 grams of coral skeleton growth in a day. In the same time, the addition of the above mentioned amount of calcium acetate solution would account for the addition of 0.7g of "extra" carbon (an equivalent of adding 4.25ml of vodka), and the formiate would account for only 0.24g of carbon (equivalent to 1.4ml of vodka).
Thus, I can mix-up an acetate/formiate solution that would be able to provide the equivalent of any amount of vodka in the 1.4 to 4.25ml range per addition of every 2g of calcium carbonate in a biologically available form.
So far, I am adding 10ml/day of the acetate solution to my 65g reef tank. If I feel I need more calcium, I'll be adding part of it as formiate if I feel I need more calcium but do not want to increase the carbon load.
I am assuming that 10ml of the acetate solution or 17ml of the formiate solution would be adding about 0.78 g of calcium, which is the equivalent of about 2g of calcium carbonate. So I assume that a daily dose of the mentioned amount of either stuff to a given tank would compensate for roughly 2 grams of coral skeleton growth in a day. In the same time, the addition of the above mentioned amount of calcium acetate solution would account for the addition of 0.7g of "extra" carbon (an equivalent of adding 4.25ml of vodka), and the formiate would account for only 0.24g of carbon (equivalent to 1.4ml of vodka).
Thus, I can mix-up an acetate/formiate solution that would be able to provide the equivalent of any amount of vodka in the 1.4 to 4.25ml range per addition of every 2g of calcium carbonate in a biologically available form.
So far, I am adding 10ml/day of the acetate solution to my 65g reef tank. If I feel I need more calcium, I'll be adding part of it as formiate if I feel I need more calcium but do not want to increase the carbon load.
So far, so good. Have been dosing 10ml (containing about 3g of calcium acetate) daily to a 65g reef tank for about a week. Unfortunately, I didn't monitor the calcium and alkalinity levels yet, the essence of the experiment was to test the effect of carbon dosing in this form.
The tank did not show any negative response so far. There was a light slimy coat on the tank walls, the water went cloudy when I wiped it, but the skimmer (Deltec MCE600) cleaned it off completely in a couple of hours.
I assume the slime coat on the walls is an indication of a slight excess of carbon dosing. There is no cyano or slimy threads in the tank. Skimmer performance was stable during the week, about the same as when dosing 5ml/day of vodka. However, I am afraid to drop the redox by dosing an excess of carbon.
Thus, I think I need to cut-off a little on the carbon share. I am going to brew an acetate/formiate mix, about 5ml of acetate to 10ml of formiate solution, dosing about 15ml/day. This will give me roughly the same amount of calcium as before, while cutting the carbon by about the third. If I can overcome my lazyness, will also try to monitor the calcium and KH levels...
The tank did not show any negative response so far. There was a light slimy coat on the tank walls, the water went cloudy when I wiped it, but the skimmer (Deltec MCE600) cleaned it off completely in a couple of hours.
I assume the slime coat on the walls is an indication of a slight excess of carbon dosing. There is no cyano or slimy threads in the tank. Skimmer performance was stable during the week, about the same as when dosing 5ml/day of vodka. However, I am afraid to drop the redox by dosing an excess of carbon.
Thus, I think I need to cut-off a little on the carbon share. I am going to brew an acetate/formiate mix, about 5ml of acetate to 10ml of formiate solution, dosing about 15ml/day. This will give me roughly the same amount of calcium as before, while cutting the carbon by about the third. If I can overcome my lazyness, will also try to monitor the calcium and KH levels...
I did the tests today. I have few corals, so I managed to elevate calcium and alkalinity significantly after just 10 days of dosing my stuff. My Calcium reading was 490 and KH=16 (both tests are from Salifert).
In the mean time, my Magnesium was quite depleted (around 1020, again by Salifert), which confirms that my elevated Calcium and alkalinity result from my acetate/formiate stuff.
I am impressed. This seems to be more convenient than using the Balling method, as instead of adding 50ml daily of THREE solutions I have been adding just 10-20ml. of ONE solution.
I'll cut off my dose a little bit and will check again in a week.
I wonder how well this method would work in a tank which is full of fast growing corals...
In the mean time, my Magnesium was quite depleted (around 1020, again by Salifert), which confirms that my elevated Calcium and alkalinity result from my acetate/formiate stuff.
I am impressed. This seems to be more convenient than using the Balling method, as instead of adding 50ml daily of THREE solutions I have been adding just 10-20ml. of ONE solution.
I'll cut off my dose a little bit and will check again in a week.
I wonder how well this method would work in a tank which is full of fast growing corals...
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