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re: more CO2 regulators

Mark Gilmore <gilmore at physics_ucla.edu> sez:
> It seems to me that a pH controller is a REQUIREMENT for any CO2 system to 
> function reasonably.
> If you are trying to save money, I would also suggest that your time 
> would be better spent working a part-time job to afford the right 
> equipment, rather than fighting with a system that is doomed from the get go.

From your credentials, you should know better than this.  An open-loop
system is only unstable as the gain approaches (or exceeds) 1.  A
heavily damped system needs no feedback, and can absorb the noise
caused by drift in its components.  I'm speaking in general terms, not
just specific to our current topic of CO2 injection sytems.

Someone trying to maintain, say, a pH of 6.7 with very soft water may
need a closed loop system.

My water is very hard, with lots of carbonate and bicarbonate. (I
don't know kH and gH numbers, but the water company says the hardness
is 18 grains).  So, its buffering capacity is quite high.  And my CO2
injection rate is quite low.  And I have oyster shells in my filter
box.  If my CO2 rate were to increase tenfold, it would cause problems
eventually, but my system can absorb even dramatic fluctuations.

I've never lost any fish due to CO2 toxicity (or a pH "crash") with my
open-loop pressurized CO2 system.  I *have* had a CO2 disaster with a
yeast bottle that suddenly increased its CO2 output one night.  I
didn't have the oyster shell in the filter at the time; I dunno if
that would have helped or not.

Best regards,