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#31
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water testing, and a chemistry lesson
Please describe what your definition of KH is.
"LeighMo" wrote in message ... Injecting CO2 into water will lower the pH and raise the KH. You're half right. Injecting CO2 will lower the pH. It *might* raise the KH if you have something in the tank that will dissolve with more acidic water. But most of us don't. Most people don't put anything in their tanks that will dissolve in the water and increase its hardness. For the vast majority of planted tank keepers, adding CO2 will not affect KH. Leigh http://www.fortunecity.com/lavender/halloween/881/ |
#32
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water testing, and a chemistry lesson
Please describe what your definition of KH is.
KH is the carbonate hardness. Yes, I know, the test kits measure alkalinity, not the actual carbonate hardness. But in order to use the KH-pH-CO2 tables, KH is carbonate hardness. Leigh http://www.fortunecity.com/lavender/halloween/881/ |
#34
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water testing, and a chemistry lesson
So introducing bicarbonate (CO2 dissolved in water at this pH mostly
takes the form of bicarbonic acid) into water will not increase "carbonate hardness"? I'm not sure I understand. Baking soda will increaase the KH. That's what I said. I was arguing with someone who insisted you could increase your KH by injecting CO2 gas into the water. Leigh http://www.fortunecity.com/lavender/halloween/881/ |
#36
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water testing, and a chemistry lesson
Dissolving CO2 in water increases bicarbonate concentration, so why
would it not increase KH? Okay, I think I understand what you're asking. Sorry, I think we hit one of those "two nations separated by a common language" potholes in the earlier post. g When you said "bicarbonate," I thought you meant baking soda, since bicarbonate means baking soda in many parts of the U.S. CO2 added to water mostly stays CO2. A fraction of a percent of it becomes carbonic acid, and that's what causes the pH drop. It doesn't affect KH, as we measure it, anyway. For chemistry meeps: http://www.thekrib.com/Plants/CO2/alkalinity.html http://www.thekrib.com/Plants/CO2/kh-ph-co2.html Leigh http://www.fortunecity.com/lavender/halloween/881/ |
#37
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water testing, and a chemistry lesson
Okay, baking soda is sodium bicarbonate (Na^+ HCO3^-), so the addition
of that will increase KH as bicarbonate concentration has increased. CO2 dissolves in water to form hydrogen bicarbonate (bicarbonic acid): CO2 + H2O --- H^+ HCO3^- Okay so you mean H2CO3. Not the bicarbonate ion -HCO3? I think there's some confusion there on those two terms. Adding CO2(acid) will never form the KH (-HCO3), a buffer in this case. The above has _no buffer_ to start with, you assume pure water. A tiny tiny amount will form H2CO3 but about 1:400 will be CO2 so most folks ignore the H2CO3. But H2CO3 is not KH. There is no alkalinity in pure water. There is no acid base buffering system either. Dissolving CO2 in water increases bicarbonate concentration, so why would it not increase KH? It does not change the bicarbonate at all. I leave a glass of water out, it has a KH of 5. I add CO2 to it, it still has a KH of 5. You are welcomed to try this yourself. The total carbon has increased when you add the gas and the pH will drop, but the KH is the same, it does not gas off or evaporate. The gas will and the buffered solution will equilibrate and return to starting pH if you stop adding the CO2 gas. Regards, Tom Barr |
#38
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water testing, and a chemistry lesson
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#39
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water testing, and a chemistry lesson
tose (LeighMo) wrote in message ...
Dissolving CO2 in water increases bicarbonate concentration, so why would it not increase KH? Okay, I think I understand what you're asking. Sorry, I think we hit one of those "two nations separated by a common language" potholes in the earlier post. g When you said "bicarbonate," I thought you meant baking soda, since bicarbonate means baking soda in many parts of the U.S. CO2 added to water mostly stays CO2. A fraction of a percent of it becomes carbonic acid, and that's what causes the pH drop. It doesn't affect KH, as we measure it, anyway. For chemistry meeps: http://www.thekrib.com/Plants/CO2/alkalinity.html http://www.thekrib.com/Plants/CO2/kh-ph-co2.html Got you. I will read these when I can find a moment, thanks. |
#40
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water testing, and a chemistry lesson
CO2 + H2O --- H^+ HCO3^-
Adding CO2(acid) will never form the KH (-HCO3), a buffer in this case. Boboo. Not right. Some is formed, but _extremely little_ will be formed in pure water. Enough to ignore it's contribution in any practical case in a plant tank. Absense of Trace metals will cause less bicarbonate to form. Regards, Tom Barr Regards, Tom Barr |
#41
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water testing, and a chemistry lesson
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#42
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water testing, and a chemistry lesson
(David Lloyd) wrote in message . com...
) wrote in message . com... CO2 + H2O --- H^+ HCO3^- Adding CO2(acid) will never form the KH (-HCO3), a buffer in this case. Boboo. Not right. Some is formed, but _extremely little_ will be formed in pure water. Enough to ignore it's contribution in any practical case in a plant tank. Okay, understood. KH/CO2/Total Carbon is a complicated ball of wax depending on what you are specifically talking about and which environment it is in. The theory is fairly well dealt with in chemistry class. But the practical matter and applying it to plant tanks is another matter. Test the KH, go to the pH/KH/CO2 table and follow it down till you find the pH you need to have a CO2 level between 20-30ppm. Add enough CO2 gas ONLY(no acids/"buffers" etc) to get this pH. That's it. Regards, Tom Barr |
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