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Lyle Babberl wrote, Monday, June 16:

>   When I refill my aquarium after partial water changes using water
>straight from the tap I get small bubbles forming on everything: glass,
>gravel, plants, and slow moving fish. I figure the water was under
>pressure and with the release of that pressure in my aquarium the
>dissolved gasses will come out of solution, aided by any slight increase
>in temperature of the new water. The gas would be normal atmospheric air
>and it goes away over night. In addition there is an increase in active
>bubbling from most of the plants in response to the new water. This is in
>the form of new bubbles being formed and released intermittently or even
>a constant stream of bubbles bleeding out of cut stems and leaves that
>have been trimmed during the maintenance. This gas, IMO, must be oxygen.
>Has anyone actually had the gas analyzed or is it a given that it is O2?
>There must be trace minerals in the tap water that cause the plants to
>increase photosynthesis. I have seen several strings in the past that
>discussed this phenom. I take it to be a good sign.

The increased output from plants could also be due to the supersaturated
gasses in the water diffusing into the plants' air channels, just as they
diffuse into the air bubbles that form on the glass, gravel, etc.

The gas that is actually produced in the plants is oxygen, but while it
resides in the plants' air channels, and while it is in bubbles rising
through the water, its content is changing to become more like atmospheric
air.  The water in the tank is close to being in equilibrium with the air,
which is roughly 21% O2 and 79% N2.  The partial pressures of O2 and N2 in
water are close to the partial pressures of these gasses in the atmosphere.
O2 in the air channels of the plant will have a higher partial pressure,
and so, O2 will diffuse out into the water.  N2 in the air channels will
have a lower partial pressure, and so, N2 will diffuse into the air
channels from the water. If you collected the stream of bubbles coming from
aquatic plants you would not find 100% O2 because of these processes.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174, in
cool Jackson, Mississippi where we have not yet reached 90 degrees.