Is the kh affected by co2?

[nirfun]

Hi,
I want to know what will happan to the kh when I will add co2 to the water.
Thank you,
Nir.

[Juan C. Nieto]

if you add co2 then H2CO3 (carbonic acid) is formed.

a) if your aquarium have some solid element of CaCO3 (calcium carbonate) in filter or substratum then it reacts with some part of H2CO3 and Ca(HCO3)2 SOLUBly is formed.
This bicarbonate will make the KH go up. The PH will go down but more slowly because carbonic acid is partially neutralized. (all these things will happen slowly in theory)



b)if your aquarium hasn´t calcium carbonate then the kh is teorically stable. The PH will go down more quickly.

[nirfun]

And the kh will stay stable?
Or maybe it will be changed down?

If you can use simple words it will be much more easier for me ;)
Thank you.

[ronrca]

I think basicly what is being said is that kh is not dependant on C02. The kh will not change if you add c02 but the ph will. The level of kh will determine the rate at which ph will drop.

HTH ;)

[nirfun]

Thank you veru much! :D

[nirfun]

You are wrong!
After checking it with some friends, co2 make the KH go down.

[ronrca]

;) All I can tell you is from what I have learned and experienced! ;) As far as I know, c02 by itself will not make kh drop.

http://www.thekrib.com/Plants/CO2/

[ReDtUrK.cOm]

Yes, your wrong! c02 has a big impact on the kh and ph. If your c02 unit is pumping to much c02 into your tank it is causes a reaction kh and the kh drops! this is then can be unstable which will then make the ph unstable. Aquarium with very low kh are subject to rapid ph shifts, and this is what kills fish. On a kh test kit you will see on the chart its 1-16 dkh and from 17.9-286.4 ppm kh. 4 dkh is stable and 1dkh it unstable and is where the ph is unstable! most of the time if you have 4dkh the ph is neutral. you would no if you had a c02 unit.

[ronrca]

If your c02 unit is pumping to much c02 into your tank it is causes a reaction kh and the kh drops! I have not heard of this......yet! 8) Do you have a link or info on this?

In any event, pumping too much c02 into your tank is never something one would do intentionally and the orginal question was not about too much c02! The addition of c02 into any tank will have an affect on ph. The final ph level will be determined by the kh level as I had mentioned before. By keeping c02 within tolerable levels recommended, kh should not be affected. Too much c02 will not only have a harmful effect on fish because of rapid ph dropping but also c02 poisoning.

[ReDtUrK.cOm]

well most c02 units, can adjust the flow of c02 thats enter's the aquarium. I have a product from dupla and in the instructions i Quote: The aquarium water should have a minimum of 4 kh as otherwise the pH value can decrease below 7(acid fall). www.dupla.com

[ronrca]

:thumbsup:

[ReDtUrK.cOm]

so nirfun, the kh is effected by c02, it will drop a little and should stablise! :)

[ronrca]

I have not heard of this......yet! Do you have a link or info on this? I just want to learn of this since is all! More directly, I want 'proof' and explanation how! ;)

[nirfun]

so nirfun, the kh is effected by c02, it will drop a little and should stablise! :)


Thank you!
Nir.

[ReDtUrK.cOm]

ok if u have a c02 unit,CO2 Dauertest and a pH Electrode and akh test kit you will be able to see how its effected!
here is a quote from www.dupla.com
. Stable carbonate hardness.
If an aquarium suffers from CO2 deficiency, the following will occur: Carbon is chemically bound in carbonates. Without sufficient 2 the plants need this bound carbon. Through the process of biogenic decalcification, the carbonates are broken down, the carbonate hardness drops to dangerously low values, and the pH value becomes extremely unstable. With sufficient CO2 supply however, the plants utilise the carbon contained in the carbon dioxide. Biogenic decalcification no longer occurs and water stability is assured.

[ronrca]

If an aquarium suffers from CO2 deficiency, the following will occur: Carbon is chemically bound in carbonates. Without sufficient 2 the plants need this bound carbon. Through the process of biogenic decalcification, the carbonates are broken down, the carbonate hardness drops to dangerously low values, and the pH value becomes extremely unstable. With sufficient CO2 supply however, the plants utilise the carbon contained in the carbon dioxide. Biogenic decalcification no longer occurs and water stability is assured.
Yes, this is true and I understand this process! However, again, the original question was if kh is affect when adding C02! The quote refers to a deficiency or lack of carbonates in a planted tank when C02 is not added.

If a deficiency in carbonates were happening and you were to add C02, yes, the kh would be affected by kh level rising again to the 'normal' level and the plants using C02 as the source of carbon instead.

I want to know the relationship between kh when C02 is added and how kh is affected when C02 is added without a deficiency of carbon!

[ChloroPhil]

Wow...what a discussion. Here's the skinny of it all with some review of previous posts for the sake of completeness.


To answer the question "Is KH affected by adding CO2 to an aquarium?"

_no_

KH is the measurement of Carbonate (CO3 2-) in the water and that measurement isn't going to be affected by the amount of CO2 in the water. Your KH remains stable as long as the CO3 molecules aren't broken down, such as happens during Biogenic Decalcification, which will actually _raise_ the KH.

Carbonate (CO3 2-)alone cannot be used for Biogenic Decalcification as it contains no Calcium, only Carbon and Oxygen. Biogenic Decalcification only occurs in environments high in Calcium Carbonate (CaCO3) and severly deficient in Carbon (organic or inorganic). The plants will absorb the CaCO3 and break the molecule down to get at the Carbon atom. The result is Calcium deposits on the leaves and Oxygen. In a system where Carbon is available readily (CO2 gas or organic carbon in the environment) the plants will use that instead. Biogenic Decalcification is much much more energy costly than breaking the O-C bond found in CO2.

Statement 2:
Yes, your wrong! c02 has a big impact on the kh and ph.

Not quite. CO2 along with KH have an impact on pH. More on that later.

If your c02 unit is pumping to much c02 into your tank it is causes a reaction kh and the kh drops!

Read below.

Aquarium with very low kh are subject to rapid ph shifts, and this is what kills fish.

Yes and no. Stress caused by large pH shifts can lead to disease which can kill fish. The drop in pH is caused by increased amounts of Carbonic Acid in the water. That Carbonic Acid is dissolved CO2. Increasing the concentration of an acid in solution lowers the pH. Therefore, as the pH lowers, the concentration of dissolved CO2 increases which will suffocate your fish.

On a kh test kit you will see on the chart its 1-16 dkh and from 17.9-286.4 ppm kh.

KH and dKH are two totally different things. KH is Carbonate Hardness and is commonly referred to as the Alkalinity (opposite of Acidity) of the water. dKH is what most Europeans use to refer to what we in North America call General or Total Hardness (GH). GH is the measurement of dissolved Calcium and Magnesium in an aquarium. It's very important to not get those two mixed up.

Check this link out for more information:
http://www.fishdoc.co.uk/water/hardness.htm

you would no if you had a c02 unit.
You'll do better around here if you're polite to people and don't make assumptions about them and what they do or don't have.


Here's a discussion of water chemistry regarding the relationships between CO2, CO3, pH, and KH. This is the chemistry of an aquarium where CaCO3 and CO2 are supplimented and are in excess for purposes of chemical reactivity.

Don't forget the states:
(g)=gas, (s)=solid, (l)=liquid, (aq)=aequeous solution
-->/<-- denotes chemical equilibrium


CO2 is added to water creating Carbonic Acid:
CO2(g) + H2O(l) --> H2CO3(aq)

Being an acid H2CO3 will dissociate and release a Proton(H+, a Hydrogen atom without the electron) into the solution forming Bicarbonate (HCO3-)
Here's the dissociation equation:

H2CO3(aq) --> HCO3-(aq) + H+(aq)

CaCO3 is added:
CaCO3(s) + H2O(l) --> Ca+2(aq) + CO3 2-(aq)

We now have in solution an acidic Proton (H+), Carbonic Acid (H2CO3), Calcium (Ca), and Carbonate (CO3 2-). These four substances will react to form and aqueous solution containing Hydronium Ions, Calcium ions, Calcium Bicarbonate, and Carbonate.

H2CO3(aq) + CaCO3(aq) -->/<-- H+(aq) +Ca 2+ (aq) + Ca(HCO3)2(aq) + CO3 2-(aq)

This actually results in the increase in the concentration of Carbonate in solution for a moment. In this system Carbonate is the conjugate base of Carbonic Acid. Those free acidic protons are quick to react with the free Carbonate to form Bicarbonate and Carbonic Acid again.

H+(aq) + CO3 2-(aq) --> HCO3-(aq)

or

2H+(aq) + CO3 2-(aq) --> H2CO3(aq)

Therefore, we have a buffered solution, which is why we use CO3 to buffer our pH. Keep in mind, this is nearly instanteous so there will be no change in KH measurable by our hobby test kits.

What we have here is a weak acid-weak base titration which will continue as long as we keep adding our acid. As we add more CO2 to our artificial environments the concentration of Carbonic Acid increases until the concentration of CO3 2- in solution (KH) is no longer able to compensate and the pH goes down.

The relationship is lograthmic, here's a link to a great visual of the correlations.

http://www.sfbaaps.com/reference/table_01.shtml

I hope that's answered some questions.

Best,
Phil

[lesley]

Hi Phil,

Great reply, I've think I've finally tied it all together!

I was getting tied up with the pH dropping as a result of co2 and then rising again if you add carbonates (in the form of bicard or calcium carb) and not thinking exactly why the pH was dropping. I wonder if others have been in the same loop as me - knowing that pH drops when an acid is added, but forgetting that co2 creates carbonic acid in the water and merely thinking of it in relation to the carbon/carbonates thing and forgetting about the acid part.

Hope I haven't undone your reply and confused things again, but your answer has clarified an issue for me.

Lesley

[ChloroPhil]

You're very welcome Lesley. If you've got more questions you know where to ask them.

[Steve_Warner]

Hi all,
Phil did an excellent job in breaking it down on the CO2/Alkalinity relationship subject and I just have a few things to add in here as I have come to understand them........and I ain't a Chemist by any means. First off, the Alkalinity is NOT AFFECTED by the addition of Co2 itself persay, but rather by the addition of ACIDS(see Phil's post). KH is a misnomer and should actually be referred to as Alkalinity, the measurement of the water's components that give it the ability to resist a pH change. Alkalinity results from the presence of Bicarbonate, Carbonate, Hydroxide AND CO2 interactions..........NOT just carbonate as the term KH (Karbonate/Carbonate) leads one into thinking. The opposite of an acid is a base, so don't let the wording confuse you when someone uses the term that a sample is Alkaline. It is just another way of expressing the fact that a sample is NOT acidic(Hydrogen-more Hydronium ions/H3O+), it is basic or above pH 7(neutral-balanced equation) due to the balance tipping in the favor of higher buffering(Alkalinity-more Hydroxide ions/OH-). Also, in order for Calcium Carbonate(such as powder) to dissolve in water, there MUST be CO2 present for the Calc Carb to first combine with Carbonic acid(composed of CO2 and water/H2O) to go into solution as Calc Hydrogen carbonate(Or Calcium Bicarbonate/ Ca(HCO3)2 ). This can be reversed with boiling and scale will form........Industrial boilers need to really watch out for this condition! Finally, Biogen Decalc will also raise your pH. Man, I wish I paid more attention in Chemistry class when I was in school............a long time ago ;) I'm tired and going to bed now...........My brain is fried ;D


Steve

[nirfun]

wow, so many answers.
I am confused.
As you can see, my English isn't well.
So, can you give me simple answer?
If I add cO2 to the water, the kH will drop?
just yes or no please ;)

[ChloroPhil]

No.

[Steve_Warner]

Hi all,
Nirfun, I have conducted an experiment (It was fun!) to learn and show the effects of CO2 addition to water's Alkalinity to answer your question. The following pic demonstrates the results of adding CO2 to my(Las Vegas, Nevada) hard, well-buffered tap water. I filled up a measuring cup(far right in pic) to the 2-cup line with my tap water. I tested small test tubes of that tap with a KH test(alkalinity) and a pH test using drop titration method. I then bubbled in CO2 from my cylinder(see next pic) to dissolve some in the EXACT SAME WATER SAMPLE and test small tubes of that as well. The following pic yields the results of that test. The 4 glass test tubes were taken from the EXACT SAME WATER SAMPLE with one difference between the 2 sets. The 2 glass tubes on the left are of the sample with the addition of CO2 bubbled into it. The extreme left tube is the pH(yellow-low) WITH CO2 ADDED, the next one to it's right is the Alkalinity WITH CO2 ADDED. Moving to the right we have the next set of 2 test tubes, beginning with the pH WITHOUT ADDITION OF CO2(The third tube from left-blue-high). We then have, to the right of that tube, the Alkalinity test. The Alkalinity test performed on both the water without CO2 enrichment and the one with it, tested out at exactly the same drop count(7). The conversion for this test was 1 drop =17.9ppm, so in both tests, my Alkalinity measured out at approx 125 ppm Alkalinity(so I guess the final answer is "NO"). The pH was very much affected in this experiment, though. There is one more really strange result to note here and I haven't tried to think about what happened here(if anything substantial), 'cause my brain is fried after trying not to confuse the situation more when writing this. Look at the Alkalinity tube WITH CO2 ADDED. It is noticeably a lower liquid level than any other tube. I don't think it was liquid loss from me testing, but who knows. I conducted this experiment twice to make sure I wasn't screwing up.

Steve

[Steve_Warner]

Hi all,
CO2 cylinder......................

[nirfun]

wow Steve, I liked your experiment :)
Thank you very much,
Nir.

[ronrca]

;)


Man, I wish I paid more attention in Chemistry class when I was in school LOL! I really wish that I would of taken chemistry in high school! :( I hope that kids can learn from our mistakes! LOL! Thanks for the detailed explainations and experiment! ;) Maybe you can post it into the thread that Phil sticky in the planted section! :thumbsup:

[nirfun]

I hope that kids can learn from our mistakes!
I am 16 years old and we are not learning chemistry in our school,
instead of chemistry we learn physics ;)

[ronrca]

:thumbsup: I also took physics in high school! Does your school offer chemistry or do you have to take physics? Can you take chemistry later? ;) Its funny because when I was in high school, I loved physics. Now, I love biology and chemistry instead! LOL! ;D

[nirfun]

LOL
My school does not offer chemistry, dont know why, but other schools do.

Also, my school offers biology.
For now, I love physics.