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Surface O2 exchange with tight top

When I was 13, how I used to love the smell of my community tank when I
would open up the top to watch the surge of air bubbles from the airstone
pushing a swell of froth at the water's edge.  The smell was moist and
clean and fresh.

I am now one week past starting my 37 gal plant tank, which is fairly
densely planted. The otos, flying foxes and cloan loaches (2 of each) are
busy; so is the algae.  I am getting excellent CO2 injection from my yeast
system right into the intake of the cannister filter, and particularly when
the sun is bright and shining in the tank in the morning, I get the
excellent bubbleage of photosynthesis from most of the plants.  The small
O2 bubbles rise to the top, and they stay at the surface for a very long
time.  At night, when I turn the lights off, the tiny bubbles of O2 are
dense on the surface, making me think of the raft of bubbles that bubble
nesters build.

My tank is an Oceanics tank, with a very tight fitting lid.  It is pierced
in only two places:  for the cannister filter's intake and return.  Last
night, before turning off the light, I sniffed the surface atmosphere in my
tank.  It had a closed up stuffy organic "smell"-not malodorous, but it was
not a refreshing smell either such as one would expect from an air mixture
that is fairly highly oxygenated.  I looked at my fish and thought, "I am
going to give you some fresh air tonight."  So I left the tank top open to
the air and shut out the light.

Here is the question:  if I am injecting CO2 all day into this arrangement,
is the O2 generated from photosynthesis really enough to keep these fish
happy?  Are tight plant tanks a good thing?  What does a healthy planted
tank with a tightly sealed top smell like?

Macon Cowles
1680 Wilson Court
Boulder, CO 80304
(303) 447-1332

A trial lawyer for the people, at work throughout the western US.