Kalk Q?

[Canadian]

Originally Posted by Aquattro

Andrew, without reading the links, this article appears to imply supplying the daily required Ca, not increasing levels. Can enough be added to increase levels beyond daily consumption? I can't read it all now, apparently my employer requests my presence

Hey Brad,

I wrote that message this morning while I was getting ready for work and now I'm at work (writing a report between patients). I'll take the time to reply thoroughly when I get home from work.

[Funky_Fish14]

Hey Guys,

Chemially (in terms of writing out the reaction), adding the acid to Kalkwasser is actually removing the alk/carbonate buffering capacity of the water. Adding acid to a base creates (water) and a (salt). Because you are not getting any CO2 in that part of the chemical reaction, no carbonate is formed. If the point of adding Kalkwasser is to increase carbonate/alkalinity, then I think the purpose is defeated by adding the acid. You will however end up with calcium ions in the water as the 'salt' formed will seperate/dissolve (this litterally means the compound dissolves into its separate elements as it is in water, not simply sitting as a 'bunch').

Allowing the Kalkwasser to simply dissolve in water (with CO2 present) will create calcium ions and carbonate ions. This will achieve both purposes at the same time.

Although there are some exceptions, like while in aquarium water, there are always other compounds present, the primary reaction with the acid will not produce carbonate ions.

Im not sure how this pans out in a 'real' setting in the aquarium, but 'mathmatically' (or chemically speaking), I dont think the acid helps to create an alkalinity buffer.

Cheers,

Chris




- I am going to ask my chem lab teacher about this in about half an hour and see what I can get. I've seen an explanation suggesting adding acid 'creates' CO2 in the water, which does not make sense. Adding an acid to water does not make CO2... - Will update.

Chris

[Aquattro]

Chris, acetic acid,CH3CO2, does in fact contain CO2. The acetate is used as a carbon source and will increase carbonates in solution.
I'll look up Craig's article on it, it will go into depth that I no longer remember

[Aquattro]

Chris, I'll assume your the Chris88 in this thread.. http://www.reefcentral.com/forums/sh...php?p=15912606

The post above your last comment explains the addition of carbon via acetate, and how it increases solubility of CaOH by 36%.

This is quoted from Craig Bingman in the Reef Aquarium, vol 3. I've also seen detailed articles by him explaining the reaction fully.

[Canadian]

Hi again Brad,

I quickly scanned through some info on the kalk slurry method and it appears the method is most appropriate for tanks without exceptionally high Ca demands. Higher Ca demand tanks would require multiple doses of kalk slurry while carefully monitoring the effect on pH. It also doesn't appear that this would be a particularly effective way of raising Ca, especially in those tanks that are either large or have very high Ca demands. I didn't see where Myka was asking about raising her Ca - I was just under the impression she is looking for a way to dose Ca and Alk without needing Mg and doing so with kalk.

However, depending on what you read there seems to be a bit of contradictory information about whether this method is best for tanks with high Ca demands versus typical demands. Some reports suggest it's good for high Ca demanding tanks where supersaturated dripping is inadequate, while other reports indicate it's best for lower Ca demands due to the effect on pH.

Here's some more info from Anthony Calfo:

http://www.reefcentral.com/forums/sh...ht=kalk+slurry

If someone was to attempt to employ this slurry method I think the most prudent course of action would be to first determine daily Ca demands, perform the necessary calculations for how much kalk slurry is needed to maintain that level, and then divide that dose into smaller ones to monitor the effect on pH. If the effect on pH is within reason (less than 0.2) then fewer and larger doses could be trialed.

[Funky_Fish14]

Sorry, but thats not me. I use the same username as this one(Funky_Fish14) on RC.

Btw Brad, you wrote the molecular formula for acetate as opposed to acetic acid in the first of your last two posts

Acetic(Ethanoic) acid does not 'contain' CO2. There are however multiple ways acetic acid may be written.

A) CH3COOH
B) H3CCOOH
C) C2H4O2
D) CH3CO2H
E) HC2H3O2

The most common/accepted forms are CH3COOH and CH3CO2H. Some prefer to write the latter as H3C2O2H because this matches the molecular structure the best. Ofcourse all the numbers would be written as a subscript. None of these forms 'contain' CO2. There is a very large difference between the molecular formula and the molecular structure. If this was true, many other substances could also be said to 'contain' CO2.

I spoke to some chemistry profs about this topic, here is where the CO2 comes from in the reaction.

Excess Ca(OH)2 reacts with the little amount of CO2 in the water to produce bicarbonate ions. Excess reactions occur (because there is no CO2) and produce Bicarbonate ions. Bicarbonate react with calcium and create Calcium Carbonate and water. The Acetic acid has a tendency to react only with the Carbonate ions that are formed, as opposed to with the hydroxide (OH) ions, which in turn produces a bunch of CO2 required for the reaction with the Calcium Hydroxide (Kalk). This explains why the acetic acid works to dissolve the kalk. That is why it allows a large dose all at once to work. However, dripping a kalk solution in to the water slowly will work fine as well, because the Calcium Hydroxide has enough CO2 throughout the aquarium water to react with and dissolve correctly.

In my previous post in this thread, I had yet to see anywhere online offer any explanation as to why the acid would not react with the base (calcium hydroxide, kalk) right off the bat. My chem profs were able to explain why it works and why it has a tendency to avoid reacting with the Ca(OH)2 immediately. This post clarrifies my last point in my last post, and why adding acetic acid works. So what I initially explained about acid not working was wrong(I knew that it did work in practice, but chemically didnt make sense?), but, apparently it takes a heck of a lot more chem knowledge to understand why its happening.

Cheers,

Chris

[Myka]

Uhm...dangit you chemists talking over my head. I'm kidding.

To clarify, I ran out of plain calcium and only have calcium with magnesium in it. My magnesium is at 1475 ppm, so obviously I don't need to add any more magnesium. So I was hoping I could just add a Kalk slurry, but from these posts it looks like I would cause too great a pH spike as I need to provide about 20 ppm calcium and 1 dKH per day.

[Funky_Fish14]

What is your pH at?