Azoo CO2 indicator question

[Chris Eriksen]

I just bought a Azoo indicator. There seem to be more than one
version of it, so click this link to see the one I have.

http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=4608

Anyway, It is not clear to me from the instructions which way the
thing is to be orineted in my tank. Is is open end down, or open end
up?

If it is open end down, Should there be a trapped air bubble between
the hole leading the indicator fluid or should I let it escape? That
would seem that the indicator fluid with just leak into the tank.



Any help would be appreciated.

Chris

[Doug]

Chris,

Understanding this device is simple if you know how the thing works...

The governing principle is that CO2 (and all other dissolved gasses) in
a small pocket of "air" in contact with the tank water will be in
equilibrium with the disolved gas concentrations in that water in
alignment with Henry's Law (the solubility of a gas in a liquid is
proportional to the pressure of the gas over the solution).
Furthermore, since this same pocket of gas is in contact with the
solution inside the device, the CO2 concentration in this solution will
eventually be the same as that in the tank. Since this solution
contains a pH indicator dye, and CO2 in water forms carbonic acid, the
color of this indicator solution changes with respect to CO2
concentration.

So, you need the bubble of gas trapped between the two solutions. Thus,
the open end should be down, and a gas bubble should be maintained
there. Also, keep in mind that this is an equilibrium device, and it
takes time for the gas bubble and the inner solution to come into
equilibrium with the concentrations of dissolved gasses in the tank, so
it will be some time before an accurate reading is obtained.
Furthermore, sudden changes won't be indicated, so all adjustments need
to be done slowly -- a good idea always, no matter your method of
detection.

Best luck!
-Doug

Chris Eriksen wrote:
>
> I just bought a Azoo indicator. There seem to be more than one
> version of it, so click this link to see the one I have.
>
> http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=4608
>
> Anyway, It is not clear to me from the instructions which way the
> thing is to be orineted in my tank. Is is open end down, or open end
> up?
>
> If it is open end down, Should there be a trapped air bubble between
> the hole leading the indicator fluid or should I let it escape? That
> would seem that the indicator fluid with just leak into the tank.
>
> Any help would be appreciated.
>
> Chris

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[Doug]

I've never used it, but I have no doubt it will work fine -- I've seen
others using similar homemade devices with a simple photovoltaic device
and a relay to control CO2 injection systems. The only caveats are (1)
remember that it is not a direct indication of the tank pH, so continue
to watch your tank pH and hardness, and (2) it will react slowly to
changes, so if things go awry quickly, you will be slow in knowing.

Eric Schreiber wrote:
>
> Doug > wrote:
>
> >Understanding this device is simple if you know how the thing works...
>
> Very clear explanation, thanks. Now, my question is, does this gadget
> actually work well?
>
> --
> www.ericschreiber.com

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Friendlies: change notmail to hotmail to reply.
Just keeping the web bots and crawlers from filling
our inboxes with junk! May they eternally spam
addresses that swamp their servers with bounced mail!

[Chris Eriksen]

Thanks for the detailed response. I now understand. As for how well
it works, we'll see.

Thanks,

Chris


Doug > wrote in message >...
> Chris,
>
> Understanding this device is simple if you know how the thing works...
>
> The governing principle is that CO2 (and all other dissolved gasses) in
> a small pocket of "air" in contact with the tank water will be in
> equilibrium with the disolved gas concentrations in that water in
> alignment with Henry's Law (the solubility of a gas in a liquid is
> proportional to the pressure of the gas over the solution).
> Furthermore, since this same pocket of gas is in contact with the
> solution inside the device, the CO2 concentration in this solution will
> eventually be the same as that in the tank. Since this solution
> contains a pH indicator dye, and CO2 in water forms carbonic acid, the
> color of this indicator solution changes with respect to CO2
> concentration.
>
> So, you need the bubble of gas trapped between the two solutions. Thus,
> the open end should be down, and a gas bubble should be maintained
> there. Also, keep in mind that this is an equilibrium device, and it
> takes time for the gas bubble and the inner solution to come into
> equilibrium with the concentrations of dissolved gasses in the tank, so
> it will be some time before an accurate reading is obtained.
> Furthermore, sudden changes won't be indicated, so all adjustments need
> to be done slowly -- a good idea always, no matter your method of
> detection.
>
> Best luck!
> -Doug
>
> Chris Eriksen wrote:
> >
> > I just bought a Azoo indicator. There seem to be more than one
> > version of it, so click this link to see the one I have.
> >
> > http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=4608
> >
> > Anyway, It is not clear to me from the instructions which way the
> > thing is to be orineted in my tank. Is is open end down, or open end
> > up?
> >
> > If it is open end down, Should there be a trapped air bubble between
> > the hole leading the indicator fluid or should I let it escape? That
> > would seem that the indicator fluid with just leak into the tank.
> >
> > Any help would be appreciated.
> >
> > Chris