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Re: Light and CO2
On Mon, 21 Dec 1998, Ole Larsen wrote:
> Hello everybody.
> On several occasions on this list have I seen the need/use for CO2
> connected to the amount of light. This might be true, but not
> nessesarily the way we all think (more light, more CO2). At last years
> symposium at Aqua Plantae Scandinavica, biologist Ole Pedersen, Tropica,
> told of some research, which at least to me, was new. The ususal
> +ACI-rule of minimum+ACI-, saying that any organism needs so many
> factors (nutrients, lights, temp., ect) fulfilled in order to grow, and
> if any of theese is in shortage, the growth will suffer. This rule does
> not always hold absolutely thruth: Some plants, about dying from lack of
> light (energy) was given extra CO2 and started growing well.
I've given some thought to this sort of behavior. I imagine that the
plants that were near dying for lack of light were maintained in an
environment that was also quite low in CO2 - something like a
well-aerated, sterile tank. Do you remember if that was true?
Aquatic plants can use either dissolved CO2 or (at least in some cases)
bicarbonate, but using bicarbonate requires an energy expenditure by the
plant. Under low light the plant probably wouldn't have enough energy to
use bicarbonate as its carbon source (assuming that it was a species
genetically capable of that trick). You can get around the energy limit
by adding a little CO2; then the plant can get the necessary carbon
without being burdened by the additional energy necessary to get it from
At least, that's the way I thought it through.
Most of our aquariums are provided with CO2 from respiration by fish,
snails, bacteria and so on. The CO2 concentration doesn't drop to the
levels you would see in a sterile, well-aerated tank unless the light is
fairly bright. Under low light conditions the CO2 supply from respiration
is usually good enough that most plants adapted to grow under low light
aren't stressed by the lack of carbon.
> And I am sorry nobody responded
> to my message on using ironsulfate. At least I would like to know why.
I think I remember your original question. I've used iron sulfate in my
garden. In addition to being an iron source, the ferrous iron oxidizes to
ferric iron, combines with water, and hydrogen ion is released to acidify
the soil. That's often a good thing in alkaline soils.
I also have some around that I've used in my aquariums. There are two
problems with it that I know of. First is that it oxidizes very quickly
and precipitates as insoluble ferric hydroxides, which reduces its
availability to plants. Second is that even extremely small amounts of the
dust create a very unpleasant metallic taste when inhaled and even the
small amount that you might have on your hands can be tasted hours after
handling it. It's pretty unpleasant.