In article ,
Chuck Gadd wrote:

On Fri, 22 Nov 2002 20:55:39 GMT, wrote:

Is CO2 beneficial for plants in a low light(1-2 wpg) application or
should it only be used in 2 wpg+ applications? Thanks,

As Tom Barr, and Claus Christensen over at Tropica have observed, even
low-light tanks will benefit from CO2 injection.

And it does make a lot of sense. Plants need Light, CO2, and
nutrients. If the light level is very low, plants need to work
harder to utilize that light. If the CO2 level is very low, plants
need to work harder to utilize that CO2. If the plant is spending its
energy to utilize CO2 and light, then that energy can't be used for
growth. So, if you supply more of light or CO2, then the plant
doesn't have to work quite as hard, and so it has a little more energy
left for growth.

At the AGA Conference, Claus showed a chart, showing differences in
growth rates based on low or high light and CO2 levels.

At low light and low CO2, the plants must expend high amounts of
resources to assimilate CO2 and capture light. The plant (Riccia in
this case) grew at a rate of 1.1% per day.

With low CO2 and high light, the plant still needs to expend high
amounts of resources to assimilate CO2, but less to capture light.
This means there is extra resources in the plant for growth. The
plant grew at 6.5% per day.

With high CO2 and low light, the plant expends high amount of
resources to capture light, but less to assimilate CO2. The plant
grew at 4.1% per day.

And when provided with high light and high CO2, the plant was able to
utilize all of its resources for new growth, resulting in a growth
rate of 14.8% per day.


Another chart showed the effects of the various levels of light and
CO2. Three levels of CO2 and three levels of light were used. Low,
Medium, and high CO2 were defined as 0.7mg/l, 6.6 mg/l, and 35.2 mg/l
Low, Medium and High light were defined as 1400 lux, 5400 lux, and
15200 lux.

At low light:
Low CO2 = 1.1% growth
Med CO2 = 3.8% growth
High CO2 = 4.1% growth (a 272% increase over low CO2)

At medium light:
Low CO2 = 3.3% growth
Med CO2 = 92.% growth
High CO2 = 10.3% growth (a 212% increase over low CO2)

At high light:
Low CO2 = 6.5% growth
Med CO2 = 10.5% growth
High CO2 = 14.8% growth (a 127% increase over low CO2)

(Note, the percent increases were calculated by me, so if they are
wrong, it's not Claus' fault!)

This tells me that CO2 can have more impact on low-light tanks than on
high light tanks.

But, in high-light tanks, CO2 is manditory, because otherwise, with
the massive amount of light, if the plants are CO2 limited, algae will
thrive.









Chuck Gadd
http://www.csd.net/~cgadd/aqua



Excellent info Chuck. Thanks!

Scott