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Re: [APD] O2 consumption by plants


The test showed 5.8 times slower dissolution for ambient(96% O2
saturation) vs 30ppm of CO2 at 140% O2 saturation(n=3).
That was for the first 3cm of the tube volume with a total of
13cm filled immediately with CO2.
The next 3cm on the other hand took much longer, virtually no
movement after 30 minutes. I reattachwed the CO2 back to the
reactor at 1 bub/3sec and the level never went up and grew
slightly by 1.5 cm over the next 2 hours.

By contrast, at ambient levels, the gas rapidly dissolved 6 cm
level in 41 seconds.

You can make what you will of this, but I did the test and that
is what I saw/observed.

Each case had ambient vs 30-35ppm CO2 late in the day as well as
freshly evacuated reactor tubes and CO2 airline/gas line/tubing
in the reactors etc(need to remove all the air).
After fresh CO2 was added, the test time began. 

So the CO2 mist that totally dissolves before hitting the
surface would now take instead of 5-10 seconds(we all know CO2
does not dissolve "instantly", be careful not to imply/assume
this) it will now take 25-50 seconds, plenty of time for the
mist to do a lap with decent current. Things are not ideal in
the tank so some will dissolve faster/some slower also.

Yep, CO2 is highly dissolvable in water, I'm not saying it is
not. But it does take __time__ and is influenced by the type of
reactor used, flow rate, bioball design, amibent/super saturated
conditions, and given that CO2 is an acid and KH is a base,
quite unlike any other gas in water. CO2 is also highly
compressible compared to other gases(external reactors do have
some backpressure associated).

Also, if the CO2 mist makes contact in the unstirred layer,
it'll will not dissolved as fast as the open water current(eg on
the left vs floating in the current).

You can also view the smaller CO2 bubbles inside a (very
recently evacuated and refilled with fresh CO2) reactor tube
persisting for longer periods. Add lots of CO2 and see what
happens(do not kill your fish). 

If you add more and more CO2, the reactor will not be 100%
efficient and most are not later in the day as CO2 levels build.
You can see them burping tiny gas bubbles.

Same for an internal reactor(simply flip it and crank the CO2
back in). 

If I were you, I'd break out the O2 test kits/meters.
That is needed to tell you the rest of the story.

O2 BTW dissolves 92X slower than CO2 at ambient conditions(over
one hour vs 41 seconds for CO2 per unit volume.

When we turn the CO2 reactor back on early in the morning, we
see the bubble disspear rapidly(seconds), with O2 is takes a
very long time(several hours).

I have gas samples from the reactors, I'll take them to a lab
later next week. I want to rule out the other gases to be sure. 

Remember that the 5.8 difference will effect the CO2 reactor's
ability to efficiently dissolve CO2 and the rate of gas being
delivered. At lower CO2 flow rates, the gas does not persist
inside the reactors. 

Basically as you add more and more CO2 ppm to water, you need
more and more efficiency from the reactor. 

Otherwise any tiny little reactor would be suitable for a 5000
gallon tank as long as it had enough current mixing.

But folks have not said a thing about some of these issue, but
200$ a bottle gas fills were mentioned but doubtfully never
followed through on.

I have a number of things I have still yet to look at on the
issue(but I'm up to my ears in research for the next week). It's
interesting and some things do _appear to conflict_ but that's
what makes it interesting.

The other thing that at the end of the day really counts is that
is does quite a number on your plants and makes them grow better
and it's a cheap easy method to add to your existing or new

I will add and modify as I work on it more.  
Tom Barr 


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