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Re: Natural Sunlight for Aquariums

On Sun, 18 Jul 1999, Craig David wrote:

> Subject: Natural Sunlight for Aquariums?
> I am posting this question for a friend of mine who is contemplating
> renovating his roof to take advantage of natural sunlight for his aquariums.

Since your friend is in Indonesia he probably doesn't need to worry much
about day length and season changes.  If you depend on sunlight in a
temperate clime you might want to augment natural light with artificial

I kept a couple tanks in a south facing window, where through the winter
they received up to 6 hours of direct high desert sunlight/day.  During
the summer the window was shaded by an eave and a large mulberry tree.  
Green water and high temperatures were problems, but you know about those.  
The pH in an aquarium can get high under bright light and without CO2
additions. I measured pH over 9 in my sunlit tanks.

I found that most aquarium plants failed to thrive under the direct
sunlight.  I think the solution is to add CO2 and/or to filter the
sunlight so it's not so bright and direct.  I think this is what

Photorespiration is a reaction that is catalysed by the same protein that
catalyses photosynthesis.  In photosynthesis water and CO2 are combined to
make a simple sugar and oxygen.  Plants live on the sugars.  In
photorespiration a simple sugar is combined with oxygen and broken down to
water and CO2, It occurs all the time in plants but normally at rates that
the plants are adapted to live with.

Low CO2 levels and high light levels both favor photorespiration.  
Photorespiration can cancel out a lot of photosynthesis when the
conditions are wrong - it might even cause the plants to burn all the
sugars they can make.  If that is carried on for long enough then the
plants starve.

In my tanks, one or two species of plants (vals and C. wendtii) appeared
to be better adapted to those conditions and they thrived.  Plants less
adapted to high light and low CO2 died.  With a different combination of
plants your friend might find a different small set a species thriving,
and all others failing.

Anubias barteri nana held on for quite a while, and even grew well through
the first sunlit season.  The nana seemed to thrive as long as the tank
held shimp and small fish that took shelter in the nana's roots.  The
critters' respiration gave the plants a fairly direct CO2 supply, and I
think that's why the nana survived.

Sunlight on planted tanks creates some really beautiful effects that I
don't think you can get any other way.  In exchange for the beauty of
simplicity you get with sunlight your friend might need to give his plants
a little extra protection.

Roger Miller