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Re: CO2 Indicators (was: CO2 Regulation)

Paul K. wrote:
"I am not a user of bottled CO2, so I am only a bystander to this long and
knotty thread, but I remember seeing or hearing about a pH measuring device
that had an indicator dye, probably bromthymol blue, in some kind of
plastic container that you submerged in the aquarium.  The plastic
apparently is permeable to hydrogen ions, but not to the indicator dye, so
that the pH can change as the tank pH changes without any of the dye
escaping.  This indicator device would be quite useful for some of the
problems mentioned, namely the drifting and aging of pH electrodes in
controlled systems and the increase of flow because the regulator is not
coping with a drop in tank pressure in systems that only use a regulator."

Dupla, Eheim (I think), ADA, and Aqarium Landscapes all make a version of
this type of  in-tank CO2 indicator device. I have both the Dupla and the
ADA versions. They all work by diffusion, but it is thru an air/water
interface rather than diffusion through plastic.

The ADA is hand blown glass and very attractive - it looks like a little
drop of crystal. The Aquarium Landscape model appears to be an exact replica
(at least from the photos), but it should be available in North America
(Robert H. or Dwight can probably get them as they both sell Aquarium
Landscape products) and considerably less expensive that the ADA model I

In operation, I prefer the Dupla version as there is a white plastic section
against which the color change due to pH flucuation is easy to see (the ADA
model is just clear glass and depending upon the background against which
you look at it, you might have problems figuring out just what color the
liquid inside is).

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

James Purchase