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My two bits on dissolved gasses and pearling
I have a hard time understanding how these gasses get into the water coming
from your tap. Here is why.
Municipal water supplies are not delivered directly into your house by a
pump (at least in the South, where freezing is not a major issue). Most are
pumped as either surface water (lakes and ponds) or water wells to an
elevated storage tank (the ubiquitous "water tower"), in which the water is
maintained at a nearly constant level. This serves the purpose of providing
a relatively stable water pressure to everyone's faucet, due to the nearly
constant height of the water column, or "head", at the bottom of the tower.
This method is much preferred over pressure supplied by mechanical pumping,
since the discharge pressure of a pump tends to fall as the flow rate
increases. There is also no requirement for complicated and expensive
pressure control systems.
While the water pressure of a "head" supplied system will also vary
slightly with increased flow rate, it will remain fairly constant within
the limitations of the piping. This stable pressure is affected by several
factors, including the distance from the tower, and the condition of the
piping (at least the inside of the piping).
Now that we have an understanding of the physical arrangement of the water
delivery system, lets get on to the discussion at hand.
Assuming that a pump with leaking seals pulls air into the system, these
gasses should be released once the water is exposed to the atmospheric
pressure inside the water tower. Any gas present in underground water
supplies are exposed to the same considerations, as is any gas introduced
in a water treatment process, such as aerating. Once inside the water
tower, there are no issues with mechanically introduced gasses of which I
One issue that may impact this discussion is holding time in the water
tower. If the water is held in the tower only briefly, the water will not
have enough time to "de-gas". Of course, this is only relevant if the water
has been previously "gassed". One indication that this situation is
relevant might be the increased pearling of plants in the summer, when
holding times may be shorter. Of course, higher summer-time temperatures
will tend to lessen the time required.
So many factors, so little time....
A couple of tests that might shed some light on this question (If we
believe that the higher CO2 levels are responsible)
1.) Increase the CO2 injection rate (without a water change) and observe
2.) Before putting the fresh water into your tank, let it stand overnight
in an open container and observe the effect.
If the first one results in increased pearling, and the second one results
in decreased pearling, it indicates a higher probability that dissolved
gasses (or unstable organic compounds) are the cause. If, on the other
hand, the reverse is observed, it would indicated that dissolved gasses are
not the culprit, but rather something else.
I can not prove that increased pearling after a water change is not the
result of higher levels of dissolved gases in the new water, I just can't
figure out how they got there. It makes more sense to me that there are
substances such as trace minerals or organic compounds in the water that
are depleted over the course of time, and adding the fresh water
replenishes some of them.
Douglas Guynn, in dry west Texas, where every cloud is cause for hope, and
every drop of rain is cause for thanksgiving.
dguynn at nwol_net
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." --Benjamin Franklin
"I would rather be exposed to the inconveniences attending too much liberty
than to those attending too small a degree of it." -- Thomas Jefferson