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Re: Need for CO2 controller [was:Nupro Needle Valves]Re: Aquatic Plants Digest V2 #944

> Date: Tue, 09 Sep 1997 10:12:47 -0700
> From: "Dixon, Steven" <stdixon at bechtel_com>
> Yesterday, someone mentioned getting more control over a CO2 setup
> with a controller.  I wonder if that is really necessary.  With a
> decent KH and a good needle valve there isn't much of a pH swing at
> night and the only thing I can think of to go wrong is a power outage.
> Any opinions?

A good needle valve is fine for short term regulation.  Unless you are
very lucky, you will not be able to find that "sweet spot" where the
long term CO2 input exactly matches the long term CO2 usage by plants
and loss to the atmosphere. And, if you're clumsy like me, you'll
probably bump the needle valve when you remove the regulator to refill
the tank and will have to readjust, probably the day after you finally
found the sweet spot <g>.

A controller lets you set the needle valve for a faster flow, making
it less sensitive to temperature variation and fumbling.  It gives you
peace of mind, at least until the first time it screws up.  

Note that with a controller, you still need to check the calibration
every so often so that probe drift doesn't get you.  The controller
will control the CO2 to produce what it *thinks* is the right pH based
on what the probe returns. If the probe has gotten dirty or is at
the end of its lifetime, the pH reading may not be the actual pH.  We
manually check pH with a good test kit every two weeks at water
changes to make sure the controller is still calibrated.