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Re: optimum CO2 levels

Steve Amor wrote:

> So, what I want to know is how the Dupla CO2 indicator works.  At what ppm
> is it supposed to turn green?  Is something in my water inhibiting its'
> function?  Like I said, it has NEVER changed colour, which (according to
> the instructions) means the CO2 concentration is less than 'optimal'.

I suppose that the indicator turns green at the CO2 level defined as
"optimal" in The Optimum Aquarium.  I don't recall exactly what that value
is but I'm sure someone else on the list can provide it.  I do recall
thinking that their optimal level was high.

Even at 8 ppm your CO2 concentration is around 20 times higher than you
would get from air alone, and 2 or 3 times higher than what you would
probably see in a normal aquarium with moderate light and no CO2 other
than the CO2 provided by fish, bacteria and so on.

If you can maintain 8 ppm in your tank then you know that you are already
providing CO2 faster than your plants are consuming it.  I'm not sure what
you can expect to get from further increases in CO2.  I get active
bubbling and rapid growth from a wide variety of plants with CO2 levels
near or under 10 ppm.  Maybe someone else can expound on the virtues of
higher CO2 levels.


> I am currently using DIY CO2 through a powerhead.


> There is virtually no surface turbulence and I certainly have no source of
> aeration.

Ok, if you still want higher CO2 levels then will probably need to add
more CO2 - maybe using more sugar solution in your DIY reactor would do
the trick.  Of course, there's always the trivial solutions.  You could
take the plants out of the tank, keep the lights off, or lower the tank
temperature to the point where growth is suppressed, but none of those
sound very interesting :).

Keep in mind that any time you see a value described as "optimum" that the
term implies certain goals (e.g., fastest growth or largest profit margin)
and in most cases an entire suite of variables must be regulated to
optimize a system.  Dupla's product line is designed to let you control
all of what they think are the important variables, and what they consider
to be optimum will probably not be optimum unless you use the rest of
their system and operate to their specifications.

Roger Miller