Re: [APD] CO2 Measurement Method

["Rory O'brien" <rory_obrien at stonebow.otago.ac.nz>]

I'm suffering similar confusion Vaughn; the other night my KH measured 6.5
and my (electronically tested) pH was 6.4, suggesting a CO2 level of
around 77ppm. Live and apparently happy fish would suggest otherwise but
there's no other buffering going on (that I'm aware of). I have dialled it
back some anyway.

Quoting Vaughn Hopkins <hoppycalif at yahoo_com>:

> I have a cork wall in my 29 gallon tank.  I also have been measuring
> 150 - 250 ppm CO2 using PH/KH table.  Being somewhat dim witted it has
> taken far too long for me to connect those two facts.  Apparently cork
> leaches tannins into the water which drops the PH a bit, making the
> PH/KH/CO2 table inaccurate.  Today I checked a water sample taken from
> the tank last night and allowed to sit over night vs. one taken this
> morning.  Last nights sample had KH of 9 degrees, PH of 7.0 - 27 ppm
> CO2.  Todays fresh sample had KH of 9 degrees and PH of 6.2 - 170 ppm
> CO2.    I think this strongly indicates that the cork is fouling up
> the
> CO2 measurement.   But, the .8 drop in PH should mean my actual CO2 is
> about 25 - 30 ppm, which the fish and plant reactions say it should
> be.
>   Any comments?
>
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