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Re: CO2 Indicators (was: CO2 Regulation)

       To: <Aquatic-Plants at actwin_com>
       Subject: Re: CO2 Indicators (was: CO2 Regulation)
       From: "James Purchase" <jpurch at interlog_com>
       Date: Tue, 12 Sep 2000 00:08:17 -0500

James Purchase wrote:

.....But I don't know how much faith I'd put in their readings...... I still
prefer my LaMotte pH kit. Of course, now that they have discontinued

I would put a lot of faith in their readings, or at least, faith in the
indicator being stable and reliably indicating the pH.  The indicator
molecule is a very stable molecule, and if it were altered in any
significant way, it would lose its color, very likely.  So, as long as
diffusion from the tank to the little vial of indicator is working, and as
long as the indicator is colored, I would trust the color to be reflecting
the pH as it has in the past.

I use bromthymol blue to test the pH of my tanks while I am adding CO2.
After about 3 days without CO2, they test blue.  After adding, they test
grass green to yellow green.  Since I introduce 3 or 4 percent CO2 into the
tank I can't get a yellow color unless I have acidic, unbuffered water.  I
use the bromthymol blue to see if I have added enough of my CO2 mix, so
that I don't waste my supply.  The bottle of bromthymol blue solution I use
to test with is about 6 years old, and it works exactly the way it did when
it was mixed up.

It is possible to use the color to get a reasonably accurate pH reading,
say, to the nearest tenth.  I have used bromthymol blue for a long time,
and have gotten quite good at recognizing the variations in color.  For
example, a sort of grayish blue is pH 6.8.  Even if you are not highly
familiar with the subtle differences in color, it should be easy to see if
your CO2 system is getting overactive and causing your pH to head down
towards the danger zone.  If the solution is yellow, take action!

Paul Krombholz, in bone dry central Mississippi