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Re: CO2 system with/without pH controller

>I don't think this symptom could be caused by running O2 >at night.
>Gasping at the surface is caused by oxygen shortage.  If >the fish are
>gasping at the surface in the morning then it probably >means that the tank
>is overpopulated and/or over fed and that you don't have >enough
>circulation to keep it oxygenated.

>Roger Miller

I am not sure I agree with this.  I have had my CO2 overdose my tank before
and the fish were at the top sucking air.  I checked it with my O2 test kit
and there was a huge lack of O2 in the water.  BTW I have a heavily planted
20 gln tank (small tanks are affected more my changes than big tanks).

>there isn't even any need to use an air stone at night >but if it makes you
feel more comfortable, by all means >use it.
>It's cheap, simple and it works 

I completely agree with Karen on this point.

>The possible problems CO2 causes (when there's too much >of it) aren't
caused by the excess CO2 resulting in too >little oxygen.  CO2 and O2 levels
are completely >independent in the water.  The problem with too much CO2
>would be a very low pH. This resulted in a noticeable
>pH swing (.4+), while leaving it running at night >results in a very small
pH shift (about .2)

>Chuck Gadd

Again I do not agree with Chuck.  CO2 does in fact relate to O2 directly.
Use common sense.  If you committed suicide by running your car in the
garage what kills you? 
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
fish at the top sucking air then measure the O2 in the tank.  I think you
can see my point.  
Yes pH does affect the fish badly so that definitely doesn't help either,
but I do know for sure that a pH fluctuation of .4 is not big enough to hurt
the fish.  My tank has been going for more than 2 years.  I have my CO2 on a
timer that shuts off when the lights go off.  The fish have not died in two
years and the plants bubble like crazy.  

Dave Berryman
20 gln heavily planted tank

Hope this helps Daphne :o)