CO2 measurement and revolution, KH referenced pH probe

Tom Barr

Staff member
Jan 23, 2005
Using similar methodology from dissolved Oxygem meters and adaption of Vaughn's KH reference solution inside a drop checker, I've taken the more accurate pH probe approach to resolving the wide ranges of CO2 ppms that the pH/Kh/CO2 table often give folks.

I wonder how folks mange that use ahem, O2 membranes, that
measure O2 and their response times?

You'll note, that I suggested to place the probe near flowing
water, much like the DO probes.

I think George Booth is perhaps the only one besides myself that
has a DO meters and is prepared to use it:)
Not sure why I did not think of that eailer dammit.

It also is very effective at determining if one vs another
method/treatment produces better plant growth than another(such
as CO2 mist vs dissolved). I have a O2 difference of about
3-4ppm at 29 C. So there's the evidence for that. Now I'll go
back and get a very accurate CO2 measure.

Of course what the hell do I know, I'm always telling folks not
to test and to watch their plants and take good care of their
water changes/dosing. haha

The two main types of membranes are sealed caps and loose films+
O ring gasket.

But here's a neat idea:

If we could get the "guts" removed from a sealed DO probe
version and add a pH probe in it's place, then add the KH ref
solution instead of the KCL electrolyte solution that normally
goes in the DO probes, then it would be ideal.
Basically use the outside seal/housing of the DO probe and the
nice threaded membrane cap but with a pH probe instead inside.

Teflon is pretty good about fouling.
The poly membranes are more prone to fouling but better and more

Simply storing the probe tip in a KCL solution every few days
etc will prevent the membrane from becoming fouled up.
So stop all that crying about biofouling:)
You can carefully wipe the membrane peroidically as well(the
teflon types)

This is a simple method and is more responsive than I thought
eariler. A little tweaking and I can get a real nice set up.

I'm going to bug Pinpoint and Milwaukee to see if they can make
a sealed screw on cap type probe like the DO version, but with a
0.01 accuracy pH probe inside.

That way I can use the nice screw on seal with the membrane
already on there and conveinence of their probes, they are cheap
as well.

I'll still need to take the pH probe out to calibrate it and add
KH ref solution back.

Then I'll go back and redo some Mist vs Reactor measurements to
see if there is a significant difference using very accurate
measurements for both CO2 and O2 together.

From there, I can make some rather strong statements as to O2
and CO2 levels in our tanks with a higher degree of confidence
and less assumptions.

And then so can others.
Vaughn has already laid the ground work for folks using the Drop
checker method, a much cheaper version and also very good for
the less techy folks.

Tom Barr