Re: [GSAS-Member] CO2 Question

[Erik Olson <erik@thekrib.com>]

On Mon, 19 Oct 2009, macker wrote:

> That works too, a steady bubble. Never worked well for me bc we travel a
> lot, 4 day stretches, etc. One thing gets out of balance, and Ive seen some
> messy things happen. Maybe its just my controller or something, you guys are
> smarter than me, but it regulates the PH 24/7 to 1/100th of the set PH,
> turning off or on, basically a digital tank that can correct its own errors
> without human interference, and time of day. It smoothes out a single
> fluctuation instantly.

Couple things.  The fact that a probe reads three digits doesn't 
actually mean those digits are accurate.  Remember also that the system is 
really regulating the pH, not the CO2.  As the chemistry of your tank 
changes (hardness in particular -- say a big piece of bogwood is slowly 
leaching tannins, or a calcerous sand is leaching carbonates), so does the 
conversion factor from pH to CO2 level.  So while you've still got a pH 
6.82 tank, the actual dissolved CO2 might be slowly going up or down.  You 
have to do a re-calibration at each significant water change.  If I 
remember right, the pH probes also drift over time and have to be 
recalibrated in those special buffer solutions, right?

There's also a hysteresis caveat.  Hysteresis = how long between the pH 
probe detecting the pH is too high & turning on the solenoid, and the 
injected CO2 dissolving and the probe reading low enough to turn it back 
off.  So if the needle valve is adjusted too low a rate, the controller 
will never shut off.  But too high a rate, then the controller won't shut 
off quickly enough and you get spikes.  And if the controller should fail 
on, the tank gets overdosed and kills all the fish.  So to do things 
right, you actually need to make the same basic adjustments on the needle 
valve that you do in a completely manual system.

A good regulator/needle valve will be rock-solid for a lot longer than 4 
days.  It should keep up a constant rate for almost the life of the 
bottle.


> I still like my idea though of filtering all your tanks fast enough and have
> all the multi-tanks water end up in one place, then use a controller to
> adjust as necessary. If that cycle repeast ast enough not sure why that
> wouldnt be a great option, unless it comes down to cost which is typically
> the #1 or 2 factor.

Multi-tank means having a common sump to serve them all, plus lots of 
plumbing and overflows.  Overflows outgas CO2.  And common water supply 
means sharing disease and some algaes from tank to tank.  That said, I 
mention these problems because I have experienced them firsthand -- I 
have two aquariums attached to a common sump, and get common CO2 there. 
Plus water stability, algae and diseases.  :)

And such a thing could very well work on an existing system like Jesse's 
(cf. 2009 Home show -- http://www.gsas.org/homeshow2009.torrent) where he 
has three cascading tanks on top of each other.

   - Erik

-- 
Erik Olson                                                        Sent from my 
crusty old Linux box
erik at thekrib dot com
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