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Re: Aquatic Plants Digest V3 #1042

Hello Hoa,

Your pH swing theory is plausible, but because Dyniar found his dead
fish in the morning, the plants could not have been producing oxygen
without lights. Thus the CO2 "poisoning" hypothesis can not be rejected

I do not know whether CO2 has the same physiological effect on fish as
on mammals, but at higher concentrations it acts in mammals as a

While CO2 will not displace O2 in water, at a certain concentration it
will "stick" to haemoglobin and prevent oxygen/carbon dioxide exchange
in the gills.



> Date: Thu, 20 May 1999 13:22:51 -0700
> From: Hoa Nguyen <nguyenh at nosc_mil>
> Subject: Re: DIY CO2 and asphyxiated fish
> >Date: Thu, 20 May 1999 09:33:53 -0400
> >From: "Dinyar Lalkaka" <lalkaka at concentric_net>
> >Subject: DIY CO2 and asphyxiated fish
> >
> >The first concrete results of my DIY CO2 experiment were visible this
> >morning: four dead Debauwi cats (Eutropiellus buffei). Their mouths were
> >wide open in the piscine version of Munch's "The Scream." pH was down to
> >5.5. The other fish in the tank were also obviously in distress. A costly
> >experiment. I think that from now on I will leave the spray bar just above
> >water level and let it create better aeration, even if that allows most of
> >the CO2 to escape. Healthy plants are nice but healthy fish are nicer.
> >
> >Dinyar
> Dinyar,
> I don't know if by asphyxiated you meant the fish died from lack of
> O2.  That is not the case.  CO2 does not displace O2 in water as it does in
> air.  If anything, the O2 content should go up with additional CO2, because
> of additional photosynthesis by the plants.  Your fish died from the pH
> swing.  If your water was better buffered (higher KH), then you could pump
> in more CO2, and both fish and plants would be happy.  The key is to
> monitor your pH well initially until you know how much or how fast to
> inject CO2.
> Hoa