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[APD] RE: CO2 off gassing

> I had an experience recently that highlights the importance of gas
exchange in maintaining CO2 levels. I let some watersprite just about cover
the surface of my tank and my pH went down from 6.6 to 6.2 (KH 4.5) with no
change in bubble rate (running 24/7), I assume from the reduced gas
transfer at the waters' surface.
> Clint Brearley
> Melbourne, Australia

Clint what happens to CO2 uptake when you block the light?
The water sprite has access to the CO2 in the air above.
The plants below do not and then they have a reduced light intensity.
How do you think this will affect CO2 consumptions?

The surface area is actually greater, although mixing below might be lower.
Still, the lower light levels would have a very significant effect.

Try it. Measure the CO2 over the course of a day and the next day place a
filter, reduce the light in some cionsistent manner and measure it without
the floating plants.

Then you can answer your question as to is it the floating plants block as
gas(not likely) or is it the reduce CO2 demand of the plants below from
less lighting.

Another problem with measuring CO2, how good of a CO2 delivery system you
have makes a large difference. I mentioned this before, a 24/7 system that
is wimpy might need to be on all the time wereas a good efficent 10 hour
system would not to hit a 20-30ppm range.
A responsive over built CO2 reactor easily hits the target ranges and keeps
it there. More powerful pumps will make this occur faster and good mixing.
"Just enough to get by" systems will not. 

But most of the gas is wasted to the off gassing in most tanks I believe as
Giancarlo mentions.  
I do not think the plants are somehow blocking the CO2 gas. The reduced
circulation perhaps, the blocking of light etc, but I do not believe the
plant tissue is blocking the CO2 from escaping as the reason for the
decline without looking at the _other factors_ more closely.

Fast responsive CO2 systems work well with light/CO2 "on" systems. 
Not so good for other wimpier set ups and some with DIY which are more
often than not, scraping by on their CO2 levels near the end of the brew
bottle changing.  

Tom Barr 

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