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CO2, pH and KH tests
I've been following the discussions regarding estimating CO2
concentration using the pH and KH table with interest. I understand the
importance of getting accurate pH and KH measurements in order to do
this. I have a question about doing pH test. What I've found is that the
pH reading of my tank water seems to change over a wide range from the
time I added the test chemical to the vial and say, 10-30 seconds
afterwards. When I first mix the water with the reactant by lightly
shaking the vial for 5 seconds, I get a reading of 6.4. If I continue to
shake the vial lightly for another 20-30 seconds, the pH reading goes up
to 7.0. Now which reading is the correct one. I assume that as I
continue to shake the vial, some dissolved CO2 leaves the water
resulting in a higher pH. But when do I know the chemical is well mixed
with the water and when is shaking too much? The vial is covered as per
the instructions (I am using a Wardley narrow range kit).
John Y. Ching (jyching at watnow_uwaterloo.ca) |
Pattern Analysis and Machine Intelligence Lab |
Department of Systems Design Engineering |
University of Waterloo, Canada |