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Re: Optimum CO2 levels?

James Purchase wrote:

This afternoon, I was re-reading the book "Aquarium Ecology, a Supplementary
Approach", 2nd edition, which was/is a Tunze publication.

In the section on carbon dioxide in the aquarium, there is a particularly
convoluted (at least, it seems convoluted to me) discussion of "bound carbon
dioxide", "balanced carbon dioxide" (a.k.a "free appertaining carbon
dioxide"), and finally, "free aggressive carbon dioxide".

The book also gives recommended levels of CO2 for at least two different
plant groups. They recommend that Crypts be maintained in the range of 5-15
mg/l CO2 and that Echinodorus species be maintained within a range of 15-30
mg/l CO2. The book gives no reference for these recommendations.

Does anyone know if any scientific studies have been done which would either
support of refute these ranges?

Bound carbon dioxide is probably in the form of carbonates, such as CaCO3.
Balanced carbon dioxide is probably bicarbonate where there is equilibrium
between H2CO3, HCO3-, and free CO2.  Free aggressive carbon dioxide is
probably when CO2 levels get high enough that carbonic acid, H2CO3, levels
become high and cause more rapid dissolving of calcium carbonate.

Although I don't know of any studies, I doubt that Crypts need lower CO2
levels than Amazon swords.  In my experience, it is the opposite.  Swords
grow pretty well for me in tanks where I do not supplement CO2, whereas
Crypts never grow very well unless I keep CO2 levels up in the 15-30 range.

Paul Krombholz, in steamy central Mississippi, where I got over an inch of
rain Saturday.