[APD] RE:CO2 & BGA

[Thomas Barr <tcbiii at earthlink_net>]

>"You might slap your head. What do plants do during the daylight? Remove
>CO2=> Causes the pH to shoot upwards. Measure the pH on a fully planted non
>CO2 tank."

>Thanks for your advice.  It is always useful and thought provoking.  But in
>the hypothesized case - essentially a soil substrate, 2 wpg, new tank,
>plants not growing much if at all - I suspect that there wouldn't be much
>variation in the average of the
>diurnal CO2 concentrations for the first weeks.  Later, sure.

Yes there would, unless the plants are not photosynthesizing, they will cause the CO2 to become depleted and this alter the pH dramatically.
Since a non CO2 plant tank will primarily be limited by CO2, this is the only thing the plants first be limited by and use up first.

Many of the normal non CO2 plants are also Bicarb users, they will remove the buffer, nab the CO2 and kick out OH's which will also cause the pH to increase. 

Soil substrate alone is not that large of a CO2 source, some no doubt, but only if there is a supply of O2........no O2, no CO2 will be produced by the bacteria oxidizing the organic materials in the soil, that is how the soil supplies CO2. This source of CO2 is relatively small, otherwise the O2 levels would be depleted and you could not keep any fish in there.  

>I also suspect that the change in the day-to-night CO2 concentrations would
>be small in such a tank compared to a high tech environment, since the
>plants would be growing at a much slower rate.

You suspect or have tried and measured?
I really do not recall my pH measurements from "a new tank", but I do not see why it would be that much different either. Unless the plants are not growing(assimilating Carbon, CO2 will be removed and that is the limiting factor.

>So in this case, control of water column nutrients and a dose of patience
>would be the only way to treat the algae problem in this case, I would
>think.
>Bill

But the tank is not limited by nutrients, it is limited by CO2, this also applies to algae, they prefer CO2 as well.
Add more plants and surface floaters. Lower light, non CO2, the algae are going to have a rough time against a horde of plants.

Regards, 
Tom Barr 



  

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