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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 
am aware.

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 
the effect.
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