Re: Pearling after a water change

[Ed & Laurie Dumas <eldumas at telus_net>]

Jim Miller and Rachel Sandage were talking about bubbling after a water
change. I have asked about this myself, and I did receive what I
perceive to be a reasonable hypothesis. The amount of CO2 and O2
dissolved in water varies due to many different factors, one of which is
pressure. Tap water has a pressure of 50 to 80 lbs. per square inch,
which is significant enough to increase the amount of CO2 dissolved in
the water.

When you take a sample of tap water and place it on your counter for a
while (in a container!), you will soon see bubbles gassing off due to
the sudden reduction of pressure. The same is true of aquariums. When
you do a large water change, you can notice bubbles gassing off on the
side of the tank.

Now this means that there is suddenly more CO2 available for the plants
after a water change. Many folks have said to me that the bubbles are
just forming on the surface of the leaves and then gassing off. I KNOW
that I have seen an increase in bubbles coming out from inside the
leaves (from pores or breaks in the leaves) after a water change, so I
am sure that the leaves are picking up some of the increase in CO2. The
effect, though, is temporary until the CO2 levels in the new water reach
equilibrium once again.

Someone also questioned where the excess CO2 would come from in a closed
system where the water does not contact the air (it is in sealed tubes).
The assumption that I am not yet prepared to make is that the system is
completely closed BEFORE the water is increased in pressure to send down
the pipes. I would like to see first hand a water pumping station to see
if some air is not also pumped into the water, which then becomes
dissolved gases in the water. At least I am fairly convinced that at
some point there would be a lot of turbulance as the water enters the
system.

Comments anyone?

Ed Dumas