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Old 04-11-2004, 05:56 PM
Margolis
 
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"Michi Henning" wrote in message
...

I agree. If you have 4 degrees KH and no other unusual buffers in the

water
(which is usually the case), you will measure a pH of 7.8, which is

equivalent
to 2ppm. So, there is nothing wrong with the chart, and the chart is

correct
whether you are adding CO2 or not. The only thing that can throw the chart
off is other buffers, such as phosphate. But to make a difference,
PO4 levels have to be way up, in the 1ppm range, which is rarely the

case.

By the way, Krause recommends a different method to measure CO2 content.
That method is insensitive to the presence of unusual buffers.

Step 1: Take small water sample with some pH indicator. Stick a straw into
the water and exhale through the straw into the water sample for two or

three
minutes. This sets the CO2 level at 60ppm. Take note of the pH reading.

Step 2: Take another water sample with some pH indicator and run the hose
from an air pump into the sampe for a few minutes. This sets the CO2 level
at 0.5ppm. Take note of the pH reading.

Step 3: Measure the pH of the tank water. The CO2 content is proportional
to that reading. As an example, if you measure pH 6.0 with the first

sample,
and
pH 8.0 with the second sample, a tank pH of 7 corresponds to 30ppm CO2,
regardless of any buffers that might otherwise confuse a CO2 test or

distort
the charted values.



You keep saying that having these other phosphate buffers is not normally
the case in an aquarium. But it seems to me that the reality is it is more
common than not. Most people don't run RO water with just the proper
minerals added. Most people start with tap water and then add phosphate and
other buffers to it to dechlorinate it and alter the ph to what they think
it should be. Not to mention all of the water treatment facilities that add
phosphates to the water.

Then you have the people that see these charts and think all they have to do
is lower the ph to raise the co2 level. So it is safest just say the chart
isn't accurate unless you are adding co2, imho. If you aren't adding co2,
then you don't need the chart, since you won't have more than 2-3ppm of co2
anyway ;o)

--

Margolis
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