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Re: [APD] Re: CO2 at night

Quoting Lief Brittan Youngs <liefy at yahoo_com>:

> The fact that plants do not asord CO2 at night is true. They only absorb CO2
> when they can photosynthesise and that is only when there is light. Also,
> they absorb oxygen at night so they can use the CO2 they aborbed when the
> light was on.  So, don't consider plants a good source of oxygen for your
> fish. If you need more oxygen use a powerhead or filter but don't rely on the
> plants.
> Amazing what I learned in college biology.
> Lief Youngs

Yes it is true that they absorb oxygen at night, but if you are injecting CO2 
and provide good growing conditions, they will produce such large amounts of 
oxygen during the day the water will become saturated. They provide more than 
enough oxygen to last them (and the fish) through the night, because they 
produce much more oxygen during the day then they use during the night. So 
despite the fact that they use oxygen during the evening, they are still good 
sources of oxygen in general. You can observe this by measuring your oxygen 
levels in a heavily planted fast growing tank at various times during the day. 

As for using a powerhead to cause bubbles to increase your oxygen, you will 
certainly outgas your valuable CO2 and if you have reached oxygen saturation 
will probably outgas your oxygen too. If you are going to do this, you 
definitely ONLY want to do it at night. At least at night your O2 levels might 
be low enough that bubbles might raise O2 levels rather than lowering them.
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