CAT.INIST.FR is an abstract of a publication that seems suspiciously like an improved way to use indicators for CO2 measurement. Does anyone have access to this to see what it is about?

There are many colormetric methods to measure CO2.

The real question is, do they provide reliable and accurate measurement?
Are they cost effective?

A light meter that measures color and intensity will run about 150-300$ at the least and that assumes that they will make it and not charge 500-1000$.

Note, the pH meter + Kh ref solution is quite accurate and relatively cheap.

Here's some thoughts and science behind CO2 sensors:

Potentiometric CO2-Sensor

Note, IR analyzers of gas phases are very inaccurate(20ppm + or - ) in most cases. If you have lots of $$$$, then you can get much better resolution.

These would be great if they had any accuracy also:

http://www.thermo.com/eThermo/CMA/PD...tPDF_30697.pdf

But that's the rub, no accuracy.

And they cost more.

CO2 specific ISE probes work well, but they are not cheap either:

PASPORT® pH/ORP/ISE with Temperature Sensor

And

Ammonia ISE Kit

Note, there are a few different ions there, you need to add various chemicals to rule out interferences by other ions, you cannot simply use some of them continuously in the tank due to the potporuii of ions we normally have in there.

Some ISE background:

IonSelectiveElectrodes

bionmr-c1.unl.edu/421-821/Lectures/421-821-chapter-23.ppt

These guys have decent prices and good selection and are helpful/knowledgable

Ion Selective Electrodes ISE

Regards,
Tom Barr

Vaughn, since the Bromo blue is colormetric, you should be able to treat it like a meter using a Spectrophotometer.
There are fairly cheap ones for sale on line for 99$ etc.

You take the sample out and drop in the cuvette and measure intensity over a specific wavelength of interest. If you are interested, I have a whole listing of chemical reagents and methods to measure darn near everything, you need a small amount glass ware and scales etc, but you can do the DIY approach like many scientist and measure 200 or more different water parameters fairly well with it.

You have the pH indicator, you just need to make a pair or 3 standard CO2 references, one is the air/water at equilibrium. You knwo the KH and the amount of pH indicator, all you need is to make a calibration curve for CO2 over a 1-50ppm range. A 50ppm CO2 reference solution would be nice.

Regards,
Tom Barr