CO2 reactor renders bubble rate irrelevant?

[vinz]

BC,

Agree with you, but I'm just saying that Chuck is coming from the perspective of amount of CO2 already dissolved (i.e. ppm), while you (it seems to me) are coming from the perspective of amount of CO2 injected (i.e. bps) to achieve target level of CO2 dissolved.

So, its how we translate the sentence. However, he does explain his position which I think it's quite clear.

It is good that you bring this up though, cause readers now know its not as simple as leaving the bps at a set level and adjusting the KH alone.

[bclee]

I have made a calculation.

At KH=0,

CO2=4.5ppm, pH=6.3
CO2=28ppm, pH= 5.5

It is still a 0.8 drop in pH. His article say the relationship don't hold at KH<1... ???

BC

[Allen_1971]

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Allen, I read Vinz's post. He seemed to say that it is not true that low KH causes pH to fluctuate.
----------------

and I agree that the title is misleading... however that is not (I believe) the myth which chuck is trying to debunk. A better title to his article could have been... "CO2 injection to achieve X ppm CO2 will not result in larger PH swings in low KH tanks compared to high KH tanks"... as you can see, thats quite a mouthful

-----------------
And, I am trying to say that low KH it takes lesser acid/CO2 for pH to swing... which also may mean that it is "easier"; for pH to change at lower KH, contrary to what Chuck Gadd's article claim.
-----------------

again no disagreement... if you add 1bps into a tank with KH3 and KH6, they will swing by different PH with the KH3 swinging more. But! thats not what chuck talked about... he never used bubble rates, he uses ppm. So if you have a KH3 and KH6 both achieving an increase of 15ppm, the swing of the PH is both the same! Yes, you may have to use a higher bubble rate in the KH6 tank, but ultimately you get the same ppm, and the same drop in PH

[vinz]

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On 1/8/2003 2:50:53 PM

I have made a calculation.

At KH=0,

CO2=4.5ppm, pH=6.3
CO2=28ppm, pH= 5.5

It is still a 0.8 drop in pH. His article say the relationship don't hold at KH<1... ???

BC
----------------

BC,

How did you calculate it?

[Allen_1971]

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chuck gadd wrote:
"This relationship will break down at extremely low KH levels (below 1 degree), when there isn't enough carbonate to completely buffer the acids present."
--------------------

BC,

what formula did you use? The formula used may have in itself made certain assumptions?

Also, chuck mentions that the relationship breaks down when there aren't enough buffers available... I think chemically you should be able to prove this yourself... If no buffers are present, then it reasons that the ph will drop more rapidly.

[jacian]

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On 1/8/2003 9:23:47 AM

Hi All,

I have changed from my previous limewood CO2 diffuser to a reactor with that spinning bio-ball. Notice that CO2 builds up within the container and the in rush of water from my pump would stir and mix the CO2 with the water via the spinning bio-ball. The rate the CO2 bubbles would only influence the size of the CO2 cavity within the reactor. Hence, wouldn't that make bubbles per second irrelevant as the amount of CO2 that goes into the tank would now depends on the stirring effect of the bio-ball?

Am I wrong?

----------------

The question is not using the bps to determind the CO2 level in the tank but using bps to determind how much CO2 you want to be dissolved into the tank.

There is a difference between a diffusor and reactor. A reactor would depend on the outflow of your filter. Say, if the outflow is good enough to dissolve 2bps, anything above 2bps would not increase the amount of CO2 dissolved, in fact I think it would decrease the amount of CO2 dissolved due to the trapped CO2 in the reactor causing the bioballs to stop spinning.

[bclee]

I use the equilibrium concentration of H+ to calculate.

CO2 + H2O <---> H+ + HCO3-

No buffering.

BC

[Allen_1971]

hehe I'm no expert so let me rationalize this out (hehe this is how myths get born )

If injecting CO2 into a system with buffers causes the ph to drop by X, then injecting CO2 into a system with no buffers by >X since there are no buffer present?

Anyway, I was flipping through your previous post and you mentioned the following

---------------------
At KH=0, 0.1% of CO2 dissociates in the water.

CO2 + H20 <---> H+ + HCO3-

The H+ will cause the pH to drop.

But with the presence of KH,

CO3-- + H2O <---> HCO3- + OH-
---------------------

I'm just curious, the first equation is easy enough to see... the second though, why do you have CO3? Have you already done some prior combination?

[bclee]

Heh... Allen, you got me.

Posted the wrong equation. That equation is for buffering with CO3--, eq CaCO3.

Bicarbonate in water will exist in the following equilibrium. 3 component will exist in the solution: CO3--, HCO3- & H2CO3.

eq.1: HCO3- <---> CO3-- + H+
eq.2: HCO3- + H+ <---> H2CO3

That is how KH buffer a solution.

Consider this equation.

eq.3: CO2 + H20 <---> H+ + HCO3-

The CO2 ppm we refering to is the left side of the equation (not the total CO2 we inject into the water). So if you inject CO2, most will exist as dissolved CO2 while some forms H+ & HCO3-.

If there is buffer present, the buffer will consume the H+. This cause eq.3 to shift the equilibrium to the RHS.

That means more HCO3+ is formed and more CO2 need to be injected to keep the CO2 ppm on the LHS. That also means if there is more buffering, more H+ will be consumed and even more CO2 need to be injected.

Now Chuck Gadd's article talks only about the resultant CO2 ppm. In fact, the KH will affect the amount of pH drop for a fixed CO2 ppm increase. But the effect is small and not capture within the 1 decimal place. If you refering only to CO2ppm, you leave out the part of the CO2 being converted to HCO3-. That's why apparently it looks as if there is no significant difference in pH drop with certain ppm increase at diffent KH value.

BC

[Allen_1971]

errrr ok if you say so.... me? I think I need to buy some secondary school chemistry books to read []

[bclee]

ehh... me not so good at composing my thoughts... sorry for being unclear in my previous posts.

It also took me some time scribbling on papers to recall & figure that... rusty already...

BC

[geoffrey]

I hate it when you guys talk chemistry. Chim. But nice to arouse some critical thinking..hehe..., this way I learn more from you folks, thanks.

[Allen_1971]

Hehehe Geoff... I hate it when I discuss chemistry too!! See you are not alone

[bclee]

Heh... I have no choice but to talk chemistry... I am supposed to be trained to do so...[:]

But after not joining the chemical/petroleum industry, all that are becoming rusty...[]

But anyway, I was taught by my prof to be critical about all the things I read. People who write books/article are not much different from us. They probably has more knowledge or expertise but that does not mean that they are always correct. Something I learn from school which I did not forget.

That's why you may find me disagreeing with a number of the articles or views.

BC

[geoffrey]

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On 1/9/2003 10:28:13 AM

That's why you may find me disagreeing with a number of the articles or views.

BC
----------------

Hey BC,

That's great. I like to hear that, in fact, we should all agree that we can disagree.

[Allen_1971]

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On 1/9/2003 5:15:07 PM
in fact, we should all agree that we can disagree.
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Hear hear!! Thats the spirit we like in this forum![] [:]

[DEA]

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On 1/9/2003 10:28:13 AM

But after not joining the chemical/petroleum industry, all that are becoming rusty...[]

But anyway, I was taught by my prof to be critical about all the things I read. People who write books/article are not much different from us. They probably has more knowledge or expertise but that does not mean that they are always correct. Something I learn from school which I did not forget.

That's why you may find me disagreeing with a number of the articles or views.

BC
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bc, join petroleum line oso no point
it's more on processes if i'm not wrong (chem eng)
this is more in the field of pure chem

and...
i fully agree with you
about the agreeing part

ok, on to the question proper
i disregard chem and calculations altogether
i use commonsense, ok? []
don't worry so much about it LAH~!
just use whatever bps you feel comfortable with

test your pH. observe your fish.
if both are ok (pH not below 6.5 or so) you can turn it up a notch
don't bother with calculating
the eqns are for a fixed system
throw in one variable and it's entirely different
do by eye
i use 7~8 for my 4ft and 2ft custom
ard 250l of water
never bothered with co2 calculations or pH
fish are doing fine
plants are ok
i am thinking that i can blast it all the way up []

but my $$ for the refills not inexhaustible
kiv that too