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Re: CO2 Indicators

On Tue, 12 Sep 2000, James Purchase wrote:

> The Dupla device that I have comes with a small sticker to place on the
> outside of the aquarium. There are only 3 colors shown, a light, yellowish
> green, rich green, and blue. No real pH values are listed. The ADA device
> comes with a color chart calibrated from a pH of 5.8 - 8.0 in 0.2
> increments. I don't know if the indicator dye is identical between the two
> devices.

It's all Bromothymal blue, the same stuff used in every low-range pH kit
out there.  I built my own out of a CPVC U-tube epoxied to a small sample
bottle (see http://www.thekrib.com/Plants/CO2/co2-pvc.html for the
original idea by Gary Bishop).  It was great for general indication, as
Paul said, normally I expected it to be green, but if it was bright yellow
I would worry (it never was), and if it was blue, I "blew" it and needed
to get the CO2 refilled.  The only problem with the U-tube was the very
slow diffusion time across the air gap.  But it was sure cheap on my grad
student budget!

  - Erik

Erik Olson
erik at thekrib dot com