[Wet Thumb Forum]-CO2 production

[perrush]

Hi all,

I was wondering how many CO2 a well planted aquarium can / could / will produce during night.

You can help me by giving me your highest and lowest pH of a single day (when the light go on and off) and also your KH value.

Additional info is appreciated too. (filtering over peat or not / aireation during night or not / ...

Perrush

[perrush]

Hi all,

I was wondering how many CO2 a well planted aquarium can / could / will produce during night.

You can help me by giving me your highest and lowest pH of a single day (when the light go on and off) and also your KH value.

Additional info is appreciated too. (filtering over peat or not / aireation during night or not / ...

Perrush

[António Vitor]

a lot!
I have one powerhead that only works at night, for some increased surface turbulance at night ...

if I didn't do something at night.. fish would die... (lack of oxigen)

I have DIY CO2, so I am not able to tell you what is my tank (fish and plants) CO2 poduction...

most of us have some sort of CO2 injection... so it's dificult to give some valid numbers...

and... what is a well planted aquarium?
that definition is very loose.

António Vitor

[MarcinB]

In my tank day/night pH changes do not excess 0,3 pH unit.

Tank specifications:
-150L (40G)
-90W of fluorescent lighting
-CO2 injection through the inlet of the canister filter (60 bubbles/s)
-pretty heavy fish load
-KH 6, GH 11
-no additional powerheads etc.

[ekim]

My PH swings are about 0.2 from morning to night. 0 surface movement, CO2 runs 24/7!

[wetmanNY]

Our pH flexibility depends on our alkalinity.

[Roger Miller]

Paul Sears has made this point over and over for a few years now. The size of the pH swing that comes from a change in CO2 -- all else being equal -- does not depend on alkalinity.

Roger Miller

[perrush]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Roger Miller:
Paul Sears has made this point over and over for a few years now. The size of the pH swing that comes from a change in CO2 -- all else being equal -- does not depend on alkalinity.<HR></BLOCKQUOTE>

It DOES depends on your KH, but only for a small part.

Your pH value has much more influence.

For example :
A CO2 production of 20 mg/L during night, will :

1) will drop your pH from 7.6 to 6.5 if the KH=2 (1.1 point change)

2) if the KH=6 that same amount of CO2 would drop your pH from 7.6 to only 6.9

3) with a KH=2 that 20 mg/L CO2 production would drop the pH from 7.0 to only 6.4 (0.6 point change)

Perrush

[Roger Miller]

Perrush,

You've lost me there some place. The formula that relates CO2, KH and pH is

CO2=A*KH*10^(6-pH)

There are different values for "A" and a few slightly different forms the formula, but they are all equivalent.

pH from this formula would be

pH=6-log(CO2)-log(A*KH)

The change in pH between two different CO2 values, CO2(1) and CO2(2) is

pH(2)-pH(1)=log(CO2(1))-log(CO2(2))

The KH values and the A value fall out when you take the difference.

Perhaps what you have done in your examples is not keep "all else equal" -- particularly, the starting CO2.

If you use George Booth's chart at thekrib -- which is easier to use for this then something like the Tropical table -- and compare the change in pH from CO2 of 5 to CO2 of 25 at different KH values, this is what you get:

KH=5 CO2=5 pH=7.5 CO2=25 pH=6.8 Difference = 0.7
KH=7 CO2=5 pH=7.6 CO2=25 pH=6.9 Difference = 0.7
KH=9 CO2=5 pH=7.7 CO2=25 pH=7.0 Difference = 0.7

These readings are all rounded to the nearest value represented on the graph, but you can see that the result is constant.


Roger Miller

[wetmanNY]

Like many people who have difficulty balancing a checkbook, I have an awed and immeasurable respect for all chemical equations-- especially when wielded so deftly to refute what might seem like an innocuous statement, even a cliche: Our pH flexibility depends on our alkalinity. Amateurishly stated, I'm sure.

Paul Sears' name is certainly one to be reckoned with. So he too is convinced that "the size of the pH swing that comes from a change in CO2... does not depend on alkalinity" is he?

I'd have thought, quite conversely, that it didn't depend on "KH" or "carbonate hardness"-- which is neither wholly carbonate nor really "hardness"-- but quite precisely upon alkalinity, or buffering.

So then alkalinity is no longer considered a measure of the "buffer" that renders pH less flexible?