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Re: Plant Bubbles

>Date: Fri, 15 May 1998 16:44:19 -0500
>From: Steve Garinger <sgaringer at pivotint_com>
>Subject: Re: Plant Bubbles

 If the warm water is
>already saturated with oxygen, the oxygen bubbles off (ever wonder why a
>bucket of warm water, especially in winter, is cloudy, then clears?
>That's why.)

Steve is probably right that the tank water becomes saturated with O2 from
the new water's released O2... and this would cause O2 from photosynthesis
to cause the pearling to start.

The bubbles in a tank after a water change, however, also occur because of
the extra nitrogen the cold water carries. There is 4 times as much N2 as
O2 in air. After a water change, all the surfaces of a tank may be covered,
including the glass.  

>The same mechanism governs the bubbles you saw when sunlight hit your
>tank.  The rate of photsynthesis increased, the plants needed to get rid
>of oxygen and saturated the water, then any more oxygen had to be
>bubbled off.

However, this DOES suggest that the tank was light limited at that point.

> If nutrients were the cause, it would
>stand to reason that bubbling would increase dramatically and
>immediately after fertilizer is added.  I've never seen that, have you?

Although nutrients may not have the cause in the examples discussed, I
think it can be the cause in some situations.

I can control the amount of bubbling in my tanks by altering the CO2
concentration. If the CO2 level is sufficient, the plants are bubbling like
crazy. In my "high" light tank (2.2w/gal <g>), if the plants are not
bubbling by noon then I knew that CO2 was insufficient. [This used to tell
me when I needed to calibrate the probe, but after getting tired of keeping
up with the automated system, I now inject the CO2 at a constant bubble
rate.] In this tank, CO2 can be the limiting factor. 

If you want regular pearling, think about increasing the CO2.

By the way, CO2 _is_ a nutrient. It is contained in higher concentration in
cold or pressurized water. So, it seems to me that a water change should
raise the CO2 concentration.  My tap water also contains trace elements, so
if the tank was limited in a particular trace element.... BINGO. However, I
can't say how quickly the plants would react to the change in nutrients.
This would be an interesting experiment for someone to run. 

As Steve suggests, therefore, my money for the described plant bubbling
(for now) is on the temporary saturation of O2 (and N2) concentrations in
combination with new O2 coming off the leaves. 

Neil Frank, AGA