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Re: O2/CO2 interaction (was CO2 system with/without pH controller)

> Not having enough O2 will suffocate your fish and they will die.  If you
> need more proof then buy an O2 test kit...run you CO2 fast until you see the

Yes, fish need oxygen.  But CO2 DOES NOT DISPLACE OXYGEN!     I just got a 
O2 test kit.  In a spare tank, with no fish or plants, just a filter moving
water around ( and dissolving CO2 ).  With CO2 (around 20ppm) and without CO2
(guessing around 2ppm) the O2 levels were exactly the same.  I wasn't able to
get the CO2 levels much higher than that (inefficient dissolving of CO2 by the
filter, and some surface disturbance by the filter), but in that range of
CO2 levels, no detectable change in O2.   I'll try to minimize the 
surface disturbance, and see if I can get the CO2 up really high, but I'll
bet that the O2 levels still won't move.

I agree with the many others who know much more about this stuff than myself,
that there must be some other factor involved in your fish gasping at the

> timer that shuts off when the lights go off.  The fish have not died in two
> years and the plants bubble like crazy.

Lots of people can make similar claims.  I run my CO2 24 hrs a day, and I 
haven't suffocated my fish yet.