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Old 08-05-2003, 04:54 PM   #11 (permalink)
 
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gsmolin,

The equilibrium level of CO2 in water exposed to the atmosphere is not 3 ppm. It's actually less than 1 ppm. The background level of 3-5 ppm that we typically see in aquariums is produced by respiration (including bacterial respiration) in the aquarium.

Aside from that (probably useless) detail, the problem of determining CO2 in the presence of other buffers is one that I've worked on. I think Paul Sears spent some time working on it, and there are one or two methods available on the web. I'm not sure I understand how your method works. Could you spell it out in painful detail?


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Old 08-06-2003, 03:17 AM   #12 (permalink)
 
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Roger,

That's intriguing, but I did measure 3 ppm in a well aerated water sample that I used in my experiments. No fish were in the sample. Nevertheless, I could have been measuring equilibrium CO2 plus some other source of hydrogen ions in the water, because it was not a distilled water sample. Like you noted, it does not change the results of the experiment, but it could possibly explain the 2 ppm error in the results of the experiment.

I shall post all the ugly details as soon as I collect them. It's a few years old, and it may be on my home computer, or I may have to try and retrieve it from Tom's Place archives.

I shall be starting a new thread for this in the "Aquarium Maintenance and Science" forum. I notice bebop has dropped out of the exchange; he may be lurking, but it's wrong to hijack his thread.
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Old 08-06-2003, 05:08 PM   #13 (permalink)
 
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Don't look at it as a 2 ppm error. Look at it as a 200% error.

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Old 08-09-2003, 10:13 AM   #14 (permalink)
 
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Ok I'm not going to bite on that, so you can just troll away.

There's a number of problems with the old posts. I contacted Tom Griffin about resurrecting the archive containing the posts at Tom's Place, and he has informed me that the aechives are lost . What a shame, since it was a lively discussion between Robert Ricketts, myself, and a number of others who are now lost too. I do have the major experiment disclosures in Word format on a hard drive- but that hard drive is on a defunct notebook computer (. There will be a slight delay while I get the lost data off of the hard disk, and until then I remain

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Old 08-14-2003, 04:33 PM   #15 (permalink)
 
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OK Roger Miller, I am posting the long form of the experiment over in "Aquarium Maintenance and Science". It's titled "Titration of a solution of two acids, humic and carbonic (long)".

[This message was edited by gsmollin on Thu August 14 2003 at 07:52 PM.]
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Old 08-15-2003, 09:16 AM   #16 (permalink)
 
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Dumb question time,

why can't we just use the CO2 test from the Red Sea test kit, or some other company taht makes one to measure CO2 directly? My Red Sea kit doesn't appear to use the KH/pH tables at all. "This test measures only the dissolved CO2 relevant to the plants, thus excluding the bicarbonate."

anona, probably missing the point completely and therefore needing clarification
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Old 08-15-2003, 11:01 AM   #17 (permalink)
 
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All of the tests commonly available measure pH in some manner. The Red Sea kit, and the LaMott CO2 kit perform a titration. The LaMotte is just like chemistry lab, where you drop KOH solution into a sample until a phenolpthalein indicator turns pink. None of these kits know the difference between CO2 or battery acid. So if there is some other acid in the aquarium, it will throw the readings off. That's the issue with peat, since it forms humic acid in the water. The extra acid shows up in the CO2 kit as CO2.
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Old 08-15-2003, 02:43 PM   #18 (permalink)
 
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<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Ok I'm not going to bite on that, so you can just troll away.
<HR></BLOCKQUOTE>

I don't look at it as trolling. It's a valid point. If I told you a hamburger was $1 and then charged you $3 would you just figure it was only a couple of bucks?

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Old 08-15-2003, 03:45 PM   #19 (permalink)
 
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This isn't about the price of hamburger. Read the post over on Aquarium Science, and comment on the whole thing. FYI the accuracy of the LaMotte CO2 kit is about 1-2 ppm, and so measuring 1 or 2 ppm can give errors equal to the reading. The accuracy of any measurement system is always specified as percent of full scale, which is 50 ppm for the LaMotte kit. Therefore, the 1-2 ppm error is 2-4% of full scale. If that is significant to your problem, obviously you will need a more sensitive titration setup.
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