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Kalk in 5.5g AGA


Mr. Fosi

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I was reading up on kalk (here and on the web) and I discovered that there are two methods that people employ when mixing their limewater: 1) Mix 1-2tsp lime/gal RO and 2) Mix lime w/distilled vinegar (acetic acid). As with all things in this hobby, there are people who are proponents of one and people who are proponents of the other.

 

Below I have quoted from a page I found and my questions are:

 

1) Does anyone here use the vinegar method?

2) What are the possible negative effects of acetate in the water other than increased BOD?

3) Does anyone want to weigh in on the chemistry? It made sense to me, but I think other eyes need to look it over.

4) Why would a person dose a small (5.5g) tank?

5) Why would a person not dose a small tank?

 

From http://www.reefscapes.net/articles/breefcase/kalkwasser.html :

Dissolving the Kalk powder in the Vinegar first will accomplish several very good things.

 

1) It will get more Calcium ions (Ca++) into the solution because you are dissolving the Ca(OH)2 in an acid instead of water, and forming Calcium Acetate, which exists as a dissociated equilibrium of free Calcium ions and Acetate ions.

 

2) The Acetic Acid (Vinegar) provides an equivalent of all the CO2 you need to avoid precipitating the newly-added Calcium ions as useless white Calcium Carbonate powder.

 

3) After all the cool Calcium ion chemistry is over, the leftover Acetate ions from the broken-down Vinegar leaves you with free organic Carbon in the water that feeds the bacteria in your tank so that it converts more poisonous Nitrates to NO2 gas (a very good thing).

 

Adding Vinegar in Kalkwasser is one of the few win-win situations for reefers -- it has a great up side and I've yet to encounter a down side to doing it. I don't know why so few reefers do it -- lack of understanding of the chemistry behind it maybe -- but a lot more are starting now that some respected reef writers have discovered it and have recommended it and even written up detailed instructions for it.

 

By the way, you should check your pH before and after you do this the first few times to make sure it is not affected by the process. It should not be a problem. Also, if you don't already have them, get and learn to use Salifert test kits for Calcium, Alkalinity, and Magnesium. The levels of all of these are related and affected by dripping Kalk.

 

The advice not to mix the Kalk too much is right on target. As the equations I posted show, if you are not using any Vinegar in the mix you certainly DO need to avoid mixing the Kalk powder with CO2 until AFTER it's dripped into the tank.

 

Look again at the equations. Both the GOOD reaction that liberates useful Calcium ions (Ca++) into your tank, and the BAD reaction that wastes the Calcium ions as solid Calcium Carbonate (CaCO3), require the addition of different amounts of CO2.

 

The problem with allowing the CO2 reaction to occur as you mix your Kalk in a container without Vinegar is that you are mixing it in a comparatively small quantity of water that contains only a very limited amount of CO2. So, instead of having enough CO2 to go all the way to useful Bicarbonate ions (HCO3-, or Alkalinity) as you want it to, the chemical reaction stops at the undesirable Carbonate ion (CO3--). This is what sets the stage for the Calcium ions to precipitate out as useless solid Calcium Carbonate while still in the mixing container -- the Kalk mixes with SOME CO2, but not with ENOUGH CO2.

 

If your mixing container contained ample CO2, i.e., enough to fully react all the Kalkwasser as Bicarbonate ions, you would indeed then want to do all the mixing with CO2 right there in the container. It's only because there's not enough CO2 present in the small container that you need to limit the mixing to avoid precipitation.

 

So, you've actually hit on one good reason WHY we want to add the Vinegar to the mixing container -- the Acetic Acid in the Vinegar provides the equivalent of enough CO2 to take the reaction all the way to the desired end products for which we drip Kalk -- that is, to produce free Calcium ions and free Bicarbonate ions in solution in our tanks.

 

By using enough Vinegar, we can mix to our heart's content right in the container, and don't need to worry as much about dripping the solution slowly into the tank. We have already driven the reaction all the way to the desired outcome, and provided ample CO2 to produce a balance of free Calcium ions and free Bicarbonate ions. This, incidentally, is why Kalk is said to be "ionically balanced" - it produces a one-to-one balance between Calcium and Alkalinity.

 

By the way, the "stoichiometric" amount of Vinegar, i.e., that amount that provides the exact equivalent of enough CO2 to react all the Kalk powder to Calcium and Bicarbonate, turns out to be about 25ml of 5% Acetic Acid per liter of saturated (0.02 moles/liter or 1.5 grams/liter) aqueous Calcium Hydroxide solution (Kalkwasser). I've used 30ml of Vinegar to a ½ teaspoon of Ca(OH)2 per liter of mix without any problem, but recommend about 15ml to those new to using Vinegar. This means that you still need to go easy on the stirring, because we are not providing quite enough equivalent CO2 to avoid SOME Carbonate ion formation if we get carried away with the mixing.

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I've never done it before but the only problem I can see is if you used too much vinegar. Vinegar is an acid and will lower your pH (actual amount depending on your buffer capatcity in your tank) so you'd probably want to dissolve the kalk in the least amount of vinegar possible. The information that you posted fails to mention that acetic acid is a weak acid and will not fully dissociate in water so you will have some remaining unreactive acetic acid left in your solution which in a small tank may cause a noticeble vinegar smell. It may be worth a try but if it was up to me, I'd just follow the instructions on kalk bottle. With a 5.5g though, you should even be able to get around using kalk in the first place with a good salt and weekly water changes :D

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With a 5.5g though, you should even be able to get around using kalk in the first place with a good salt and weekly water changes.

 

Right, I know that I don't need to do this in my tank, but I am thinking about trying a very dilute, non-vinegar solution as my topoff 1-2 times per week.

 

I want to get people's opinions on this particular method because I found it in a bunch of places, none of which dealt with nanos.

 

EDIT: I am not sure that I agree that some of the acetic acid will be left in solution. It will be encouraged to dissolve more fully when you intruduce a strong base (OH).

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Acetic acid is an organic acid, and like most organic chemicals, just plain and simple will not fully dissolve in a solution (organic compounds are primarily covalent bonds making it harder to 'break' a substance appart for solvation to occur). A strong base will interact and remove some of the dissolved substances forcing the reaction to reastablish equillibrium at which point all of the acetic acid will not be consumed. If you ever take an organic chemistry class you'll learn in the first weak that organic reactions never happen at 100%, with anything even over 80% yeild being a good experiment.

 

Just to put it in perspective. In chemistry all acids have an associated Ka value which is essentily a number that represents the acid's solubility.

A weak acid is an acid that does not fully ionize in solution; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissolved HA still remains. The equilibrium concentrations of reactants and products are related by the Acidity constant expression, (Ka): ([H+] [A-])/ [HA]

The greater the value of Ka, the more the formation of H+ is favored, and the lower the pH of the solution. The Ka of weak acids varies between 1.8×10-16 and 55.5. Acids with a Ka less than 1.8×10-16 are weaker acids than water. Acids with a Ka of greater than 55.5 are strong acids and almost totally dissociate when dissolved in water. The vast majority of acids are weak acids.

 

The hydrogen (H) atom in the carboxyl group (−COOH) in carboxylic acids such as acetic acid can be given off as an H+ ion (proton), giving them their acidic character. Acetic acid is a weak, effectively monoprotic acid in aqueous solution, with a pKa value of 4.8. A 1.0 M solution (about the concentration of domestic vinegar) has a pH of 2.4, indicating that merely 0.4% of the acetic acid molecules are dissociated in solution.

 

Now on to the this method being used with nano parts. The reason why you wouldn't need to use this method with nanos is because the amount of kalk needed to raise your Ca levels is so small due to the tank size that it doesn't require you to use a lot of kalk in the first place so there isn't much need in increasing the kalk solubility. In a larger tank it is more to your advantage to raise the solubility of the kalk to help keep you from using so much to dose with.

 

Hope that helps out a little. Its kind of hard to explain the chemistry involved because I don't know your back ground in chemistry but let me know if that helps.

 

edit: Wikipedia had a better definiton than I used :)

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Yes, of course organic reactions never go all the way.

 

But when acetic acid dissolved in water (CH3OOH + H2O -> CH3OO- + H3O+), its first H+ ion will be the only one that reacts unless it is in the presence of a strong reducer, such as OH. Thus, should it not react 1:1 with OH unless you really bump up the OH concentration?

 

The Ka value for acetic acid = 1.8 × 10–5 at 25°C, which should give you ~1% dissociation at 0.1 M (25C). So, depending on the concentration of acetic acid in the vinegar, could you not just add slightly more CaOH and have it proceed to near completion? Completion being defined as getting most first stage H+ ions to react.

 

I've actually had two organic classes, but they were about 3 years ago.

 

In the text that I quoted, the got the impression that they guy wasn't just using the CH3OOH to increase the per volume concentration of Ca++ ion, but also to keep the dose from elevating the pH too much. Initially, I thought that idea of cutting the pH of your limewater down would be a good thing, but as you pointed out, this is probably not needed for a nano.

 

I could just as easily use less lime in a greater volume of water instead of trying for saturation like most people do.

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I would read this article by Randy Holmes who is highly respected in the reef chemistry bus.

http://www.advancedaquarist.com/issues/nov2002/chem.htm

kalk is a balancing agent and will raise your calcium it should really only be done as needed and to keep your alk up you should use baking soda/washing soda depending on your ph.

It's really for corals from what I understand they take it into there tissue which is best accepted at around calcium 450 and alk 9-10 ish I don't know the specifics so someone Else may want to weigh in.

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In theory it would work but you have to remember that reactions always work in both ways and OH- is not the only anion in the solution for the H+ ion to react with. With the reaction occuring in water there would be an infinite amount of H+ ions in solution for the COOH- to react with. There are multiple reactions occuring in multiple directions for it to be physically possible in the known realm of chemistry to consume the entire amount of HCOOH without including a substance that would ppt the COOH- ion completly out of the solution. The problem is that the reaction causes all of the ions to remain in solution, free to react with one another.

 

The reactions should be written as the following:

HCOOH + H2O <--> H3O+ and COOH- (very little of this reaction occurs to begin with)

H30+ + OH- <--> 2 H2O

Ca(OH)2 + 2 H3O+ <--> Ca++ + 4 H2O

Ca++ + 2 COOH- <--> Ca(COOH)2

 

Every time you are able to free H+ from the COOH- ion, you end with a free radical COOH- in solution that will redially react with any cation present, which in some cases may be the very H+ you seperated in the first place. Acetic acid is a weak acid because its solubility is so low that once it is dissolved it redially reacts back with the H+ in the solution or recently freed H+ radical that you are not able to put a dent in the intial HCOOH concentration past a certain point.

 

In a larger volume of kalk for a larger tank you would be able to effective dilute the unreactive HCOOH to such a small concentration that you wouldn't be able to notice it, but I think it would be far more noticable in a nano.

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There's no problem chemically with using vinegar... the problem is biological.

 

Many (including myself, onthefly) experienced bacterial blooms because the acetic acid acts as a nutrient source in a similar manner as vodka. The practical effect is snot-like strings of bacteria covering everything. Not everyone experiences this, but many do. I'm surprised it wasn't mentioned in the in-depth quote above.

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I just noticed that I used the wrong formula for the acetate ion and should be CH3COO- but oh well, was kinda late :happy:

 

I guess the real issue is what MrAnderson pointed out, the acetate acts as another nutrient source in your tank.

 

"3) After all the cool Calcium ion chemistry is over, the leftover Acetate ions from the broken-down Vinegar leaves you with free organic Carbon in the water that feeds the bacteria in your tank so that it converts more poisonous Nitrates to NO2 gas (a very good thing)."

 

So you could consume all of the vinegar at a rate proportional to the amount that the bacteria in your tank could metabolize.

 

If you want to try something different without adding any additional chemicals to your kalk, you could create a supersaturated solution. Get some DI water and place it in a pot and boil it on your stove. Add as much kalk to the boiling water while gently stirring until it stops dissolving. As the tempeture increases, so should the solubility of the CaCO3 so you'd like to have as much kalk dissolved in solution as possible. Let the solution boil for about 5 mins then remove it from the heat and let it cool to room tempeture. Let the solution cool to room tempeture as slow as possible without stirring or moving it and you'll prevent the CaCO3 from precepitating back out of the solution. If all goes well you'll end up was a kalk solution that has more CaCO3 dissolved into solution than should be possible under normal conditions at room tempeture. In the end it may turn out to be not a whole lot more than the normal way but I wouldn't be able to give any numbers without actually doing it. You may be able to do it and test the concentrations with a Calcium test kit to see the difference.

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3) After all the cool Calcium ion chemistry is over, the leftover Acetate ions from the broken-down Vinegar leaves you with free organic Carbon in the water that feeds the bacteria in your tank so that it converts more poisonous Nitrates to NO2 gas (a very good thing).

 

Adding a carbon source is helpful, but not sufficient, for increased denitrification.

 

That statement is true if you can provide an anaerobic environment to exploit that metabolic pathway. However, being facultative anaerobes, those bugs won't denitrify without unless you provide the proper environment. Otherwise they just aerobically respirate.

 

Adding carbon sources without other fine tuning can lead to an imbalance in a tank's microbial population.

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That statement is true if you can provide an anaerobic environment to exploit that metabolic pathway. However, being facultative anaerobes, those bugs won't denitrify without unless you provide the proper environment.

 

I thought about that when I read it. It would be more likely to occure in a larger tank with a DSB and dead spots in their rockwork.

 

weatbre: Thanks for the link, I am going to give it a read.

 

AMichael: Other than the mistake with the acetic acid formula, I think your chemistry is sound.

 

So the answer to my quaestions are as follows:

 

1) Q. Does anyone here use the vinegar method? A. No, but they have in the past.

 

2) Q. What are the possible negative effects of acetate in the water other than increased BOD? A. Could cause a bacterial bloom.

 

3) Q. Does anyone want to weigh in on the chemistry? A. The chemistry wasn't incorrect, just incomplete. It will be difficult to get the reaction to completion without precipitating Ca(HCO3)2. There really is no need to use a low pH solution to dissolve the CaOH for such a small tank.

 

4) Q. Why would a person dose a small (5.5g) tank? A. To allow their corals and other calcerous organisms to thrive.

 

5) Q. Why would a person not dose a small tank? A. Becuase it will be hard to balance in such a small water volume. There is a greater chance a serious problems.

 

Do you think that it would be useful to dissolve a small amount of CaOH in my topoff water and slow-drip it into the tank during the night to help control nighttime pH drops?

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Couldn't hurt but then again you would be better off using a buffer that contains Calcium if the intent is to stabalize your pH.

 

And Calcium Acetate is Ca(CH3COO)2 and not Ca(HCO3)2 ;)

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And Calcium Acetate is Ca(CH3COO)2 and not Ca(HCO3)2

 

Right. I was talking about Ca bicarbonate precipitate, which is why I said Ca(HCO3). I thought Ca(CH3COO)2 was soluable in water...

 

What is a good buffer containing Ca?

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Calcium bicarbonate and calcium acetate are both very soluble in water so I didn't quite understand where it came from.

 

As far as buffers go that contain Ca, the only one I know for sure is Kent's Tech·CB parts A & B which is a mixture of

Part A: deionized water containing the following ions: calcium, chloride, magnesium, strontium, bromide, lithium, rubidium, nickel, chromium, zinc, copper, cesium, iron, manganese, cobalt.

Part B: deionized water containing the following ions: sodium, potassium, bicarbonate, carbonate, borate, fluoride, iodide, molybdate, selenate, vanadate, and tungstate.

 

You should be able to find some others if you don't like Kent products. I think we both understand the same thing, but we're saying it in two different ways. :D

 

edit: Just noticed that its odd that they include copper in part A

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I think we both understand the same thing, but we're saying it in two different ways.

 

You're probably right.

 

I'll check out that kent stuff and see what it costs.

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Do you think that it would be useful to dissolve a small amount of CaOH in my topoff water and slow-drip it into the tank during the night to help control nighttime pH drops?

 

Many people drip kalk at night for this very reason.

 

If you're interested in dripping kalk, find out if you need to use vinegar before bothering.

 

Many tanks with a low Ca demand can get away with 1 tsp/gal of kalk. You can increase this if the demand is not met. If after 2-3 tsp kalk the demand is still not met people usually turn to vinegar to manipulate the pKd/pKa of CaOH. AMichael mentioned another common method for manipulating association/dissociation equilibium constants, temperature.

 

However, from my recollection of aqueous equilibrium of CaOH, saturation is reached fairly easily and supersaturation can be pushed only so far.

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