Time for CO2 to reach correct level

scottward

Guru Class Expert
Oct 26, 2007
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Brisbane, Australia
Hi,

Like a lot of people, I have my CO2 come on about an hour before the lights come on.

I am not sure though whether after 1 hour the CO2 has reached sufficient saturation.

I gave up using drop checkers because of the way they can be misunderstood, slow response time etc.

Could I draw any conclusions as to how 'fast' the CO2 is kicking in based on pH measurements alone? For example, if I measure the pH as the CO2 comes on, and then 1 hour later when the lights come on, measure it again, could I draw any conclusions based on the colour shift? i.e. I don't really care what the actual value is, rather, the change alone?

If CO2 is being injected effeciently, what would this change typically be? I have heard it should be 1 unit of pH, so, I guess if it measured something around 7 at CO2 on and then about 6 at lights on 1 hour later, that would be pretty good?

Scott.

P.S. If CO2 can measure differently at different locations in the tank using a probe, does this suggest that pH various throughout the tank too?
 

dutchy

Plant Guru Team
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Jul 6, 2009
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Hi Scott,

The change alone would be very visible in pH measurement...that is, depending on how accurate your test is. Still I don't think it's very useful. the colour charts from the test kits don't show increments of 0,1 pH, while 0,1 pH is a 10 ppm difference in CO2.

That's why I use a pH controller. I don't care about the number it says, but it gives me a constant value and will adjust automatically as plants grow. The setting is based on fish going to the surface, not on the pH/KH table.

When my CO2 switches on in the morning, the pH is 7,1. One hour later it's at the fixed setting of 6,5. That's only a 0,6 difference. If I go down to pH 6,1 I will kill my fish.

I've measured pH differences of 0,1 to 0,2 at different places in the tank, which would indicate 10 to 20 ppm variance in CO2.

regards,
Dutchy.
 

Tom Barr

Founder
Staff member
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Jan 23, 2005
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Would this same decline in pH have any difference on fish if the O2 also was changed?
Say if the O2 was 4ppm in one treatment and 8ppm in another?

Would the fish respond the same?
What if you had 2-3x the plant biomass blocking the current andf flow, surface turnover or the filter clogged?
Would that have any effect on the O2?


Regards,
Tom Barr
 

dutchy

Plant Guru Team
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Jul 6, 2009
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Yes...yes....and.....yes. But when you're already at more than 8 ppm of O2 there's not much to gain in O2. If you're adjusting your CO2 while you might have a clogged filter or other things blocking flow, to me it looks like doing things backwards.
 
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