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RE: article on Tropica's web site

> Look at 
> http://www.tropica.com/go.asp?article=142
> Regards,
> Claus


Great article.
Very well done!

I would add from my end concerning CO2 and lower light:

*Light limiting* instead of CO2 limiting(non CO2 tanks) or nutrient
limited(PO4/NO3, Fe) results in:

The usage of the light is much more efficient(fully utilized), therefore
more plant growth/mass per watt. This lowers electric cost, bulb cost,
initial set up cost for the lighting.

Why have efficient lighting if you do not use it efficiently?

Maintenance is considerably easier since the growth rates are slower(but not
that much) and there's less dependence on frequent dosing of N03, P04, micro
The slower growth allows the nutrients to be allocated to where they are
needed in the plant organs(e.g. roots to leaves) and tissues.
This allows better use and allocation of both the water column and the
substrate and also allows more flexibility in dosing techniques such as
substrate only dosing for nutrients.

The plant's themselves look better in many cases. Fuller foliage, better
color in some cases. Certain plants tend to have a more desirable appearance
with higher light but most seem to look bigger and have better color from
the plants I've had.

Perhaps a "light limited" aquarium is perhaps a better goal to achieve good
efficient/easy to maintain healthy growth.

I will say that limiting the light rather than limting CO2 like so many
going the non CO2 routes often do, results in much more desirable plant
growth, greatly increased plant choices and gets 100% usage of the lighting.

I have found the algae growth is far less as well than the higher light, CO2
tanks. Comparable to that of a well run non CO2 tank(meaning not cleaning
the front glass but every 1-6 months).
Plant trimmings every 2-3 weeks instead of weekly.

Crypts look very good in these tanks and plant choice can greatly reduce the
trimming frequencies also.

To bolster this concept further I made a list differentiating low light
"shade" leaves and high light "sun" leaves. This concept can be applied to
low light aquariums vs high light aquariums.


> Characteristic:       Low light:          High light:
> Irradiance at
> light compensation*    low(.5-2)            high(50-100)
> Irradiance at
> light saturation       low(10)             high(1500-2000)
> Rates of dark    
> respiration              low                 high
> Quantum yield           same or high       same or low
> Leaf thickness         thin                 thick
> Number of stomata       low                 high
> Stomatal conductance    low                 high
> Thylakoids/granum       many(100-200)      few (5-10)
> Orientation of grana    random             horizontal
> Photosynthetic e.t.
> components per unit     small               high
> Chl
> Chl a/b                 low(2.5)           high (4)
> Total Chl 
> unit area               low                high
> Total Chl        
> unit leaf weight        high               low
> Chl/photosynthetic      higher             lower
> unit
> Soluble protein
> (Rubisco) per unit
> leaf weight or area     low                high(10X)
> Rubisco activity
> per area, weight or     low                high(4X)
> Chl
> Photosynthate leaked    low                high
> into environment
> Basically at lower light, plants are more efficient. Photoxidation is less a
> problem, the plant has more time to relocate nutrients from old tissue to
> new tissue or from root to shoot. Leaf area generally increases, less
> nutrients are required to run photosynthesis, less proteins, enzymes etc to
> grow. The plant afford to wasteful at higher light, but if things fall below
> the light compensation point, the plants will die. PCP is where the quatum
> yield is less than respiration. Intake of the "plant's food" is less than
> the energy/maintenance requirements of the plant.
> It makes sense not to have all this extra photosynthetic machinery hanging
> around if there's not the light to run it. It takes a lot more energy to
> maintain all that machinery. If the plant has only a small efficient
> photosynthetic machine, it won't need to allocate the respiration /
> photosynthate to maintenance. Growth is slower but less wasteful.
> Considering electrical cost(some of us are sensitive to this issue),
> efficient use of lighting, since it's often the biggest source of electrical
> usage, is not a bad goal to consider.
> Better nicer growth, less algae problems, lazy dosing, less pruning etc may
> be something many are looking for. Lower electrical cost certainly are for
> myself.
> Enjoy.
> Regards, 
> Tom Barr 

Tom Barr