# Driftwood & CO2 Calculations...



## TetraFreak (Mar 15, 2006)

I'm getting ready to add CO2 and was wondering what effect driftwood has in altering CO2 calculations?

Since adding driftwood, pH has dropped a bit as it leaches tannins into the water. What I'm concerned with is the proper calculations with the altered pH.

Does driftwood modify pH based on carbonates or ?????

is there a good wat to properly calculate for CO2 that takes this into consideration?


Thanks in advance!

-TF


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## carpguy (Feb 3, 2006)

Tannic acid from the driftwood may depress the pH: its not related to the KH.

You can measure the pH of the water in the tank and then measure another sample again a day later after it's had a chance to offgas. That way your only measuring the change in CO2: other acids and noncarbonate buffers don't enter into the comparison, its just a measure of what's offgassing. (Assuming ambient is about 3 ppm) a drop of one full step in pH (from 7.5 to 6.5, for instance) should give you about 30 ppm.


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## TetraFreak (Mar 15, 2006)

Well, the pH out of tap is at ~7.6

Water in tank with driftwood is ~7.2

So the driftwood is dropping the ph by ~0.4

what should I base the CO2 calculations on???
The "out of tap" numbers or the "In-Tank" numbers?


Just trying to make sure I get everything cleared up before I start injecting CO2!


Thanks,

-TF


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## slickwillislim (Oct 11, 2005)

I believe if you leave a small amount of tank water by itself overnight then test the ph value that that water has needs to be dropped one number to get enough co2. I read this some where maybe someone more knowledgable can explain it better. So if the sitting water has a ph of 7.2 you want your tank at 6.2. The problem is the water at the beggining of the week would naturally be a higher ph then after 7 days with the driftwood. 

Long story short I would look at your fish and your plants and change it (slowly) to suite your tank.


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## Scoutmaster Steve (Jan 12, 2006)

If you haven't added CO2 yet and you show 7.2 in tank after the effects of driftwood, rock whatever then that would be your outgassed point. so drop your Ph to 6.2 should give you 30 ppm.


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## Bert H (Mar 2, 2004)

Take a sample of your tank water and let it sit out on the counter top for 24 hours. Measure the pH. Whatever reading you get, your target should be 1.0 pH unit below that to put you around 30ppm CO2. However, make sure you kh is 3 or above.


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## TetraFreak (Mar 15, 2006)

I tested everything last night...

Right out of the 55 Gal...
pH 7.2
kH 4*
GH 7*

My Non-Driftwood tanks:
pH 7.6
kH 4.5
GH 9

I'll be setting a bowl of water from the 55 Gal aside tonight for testing tomorrow so I'll have readings that way tomorrow evening.


Now, why would driftwood drop the water hardness like it has? Does driftwood eat carbonates?


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## jude_uc (Feb 7, 2006)

The driftwood provides organic acids. The way alkalinity works is you have a much of buffer (usually carbonates and bicarbonates, but plenty of other things buffer). Generally speaking, buffers resist pH change. Your alkalinity kit has an indicator and an acid in it. You keep adding drops and when the color changes, it is a measure of how much acid is necessary to overcome the buffering capacity. Since the driftwood adds organic acids, some of that buffering capacity is already used up keeping the pH stable against the contribution of the driftwood. So, it doesn't necessarily eat the carbonates as much as give the carbonates more hydrogen ions to work with. I think that's the dominant effect at least.

-Adam


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## TetraFreak (Mar 15, 2006)

OK, I tested the "gassed off" water and here's the results...

pH 7.6
KH 4
GH 11

Why would the GH increase but the KH remain the same???

Now, when calculating for CO2, I'd ude the 7.6 value...Right???


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## Bert H (Mar 2, 2004)

> Why would the GH increase but the KH remain the same???


 Sorry, but can't answer that one. 



> Now, when calculating for CO2, I'd ude the 7.6 value...Right???


 Yes. You want to shoot for an in-tank pH of 6.6 with the CO2 injection.


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## TetraFreak (Mar 15, 2006)

Awesome!

Thanks for the help! 

Now I'm a bit perplexed with Chuck's CO2 Calculator chart showing some different numbers...

I'm beginning to think I need a phd in chemistry to understand all of this!


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## hoppycalif (Apr 7, 2005)

Chuck's CO2 calculator is based on the equation for PH/KH/CO2, and was set up when 20 ppm was considered the ideal CO2 amount. I don't see any problem with that calculator other than the problem of having water with non carbonate alkalinity and/or non carbonic acid acidity in it. Using the 1.0 PH drop method for arriving at 30-40 ppm CO2 (actually it is 10 times the amount of CO2 in your outgassed sample, which is probably about 3-4 ppm) works around the odd water problem.


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