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[APD] Re: CO2 off at night

John T. Fitch wrote:

>Sorry, but this is not what happens in my tank.  At night, when there is
>no CO2 added to my tank, the pH does *not* go "up as CO2 diffuses out of
>the tank."  The pH goes down from 6.9 (my controller set point) to 6.7 or
>6.6.  How would this be possible if the *net* flow of CO2 is out of the

I can't explain this. 

I watched both our 100g tanks last night when the lights went out. The pH 
slowly rose when the lights went off, just as it does when the lights are on. 
When it got to 7.05, the controller turned on the CO2. When it got to 6.95, the 
controller turned off the CO2. 

>In the morning, when the lights come on, the pH level slowly rises over an
>hour or two back up to 6.9.  At that point, the contoller turns the CO2 on
>and off for the rest of the day. 

In the morning, our pH was still cycling between 6.95 and 7.05. 

>Earlier, I tried to explain what I thought was happening.  Now I am only
>reporting what actually happens.

I believe you but I can't explain what's going on in your tanks. Perhaps our 
trickle filters lose enough CO2 that the consumption/generation of CO2 by 
plants is insignificent by comparison. Even though they don't lose much more 
than other filtration/water circulation techniques, of course. 
George Booth in Ft. Collins, CO (gbooth at frii dot com)
 The website for Aquatic Gardeners by Aquatic Gardeners
   http://aquaticconcepts.thekrib.com/  (mirror)

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