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Re: NFC: DP Frozen pond question

-----Original Message-----
From: Dwight Moody <dwightmoody at hotmail_com>
To: nfc at actwin_com <nfc at actwin_com>
Date: Monday, January 18, 1999 12:15 PM
Subject: Re: NFC: DP Frozen pond question

>At a recent meeting of the Tropical Fish Club of Burlinton (VT), a
>speaker had an excellent idea.  Simply place a good size air pump (such
>as the  Luft pump or another air pump for large tanks/deep water
>applications)  in a  water proof box, place  a "breather" tube in the
>top of the box (to get access to air above the snow - bend over the end
>of the tube in a upside down "U" to keep snow  out of the box) and hook
>up to an airline and weighted airstone and outside service power cord
>(connection inside the box to prevent shorting).  Plug in and you
>provide lots of oxygen with no shoveling or chopping ice.

There might be some danger in agitating the water during freezing weather.
Under most circumstances, warm water is less dense than cold water, and so
any temperature stratification will cause the temperature at the surface to
be higher than the temperature near the bottom.  However, water reaches a
maximum density at 4 deg C, and below that point the situation is reversed.

At temperatures near freezing, the coldest water tends to rise to the
surface, while the water near the bottom is warmer (by as much as 4 deg C).
If you start agitating the water, you may prevent ice from forming at the
surface, but you will probably cool the entire body of water to the freezing
point.  Some native fish might be able to handle this, but I doubt that all
of them can.

If the setup is arranged so that the air is injected under the ice at the
water's surface, then the air bubbles won't cause convection and mixing, and
the bottom layers of water will stay warm.  Or, you could make the air
bubbles travel upward through a series of baffles, so that the bubbles make
contact with the water without dragging much water upward with them.

[\   Andrew Dalton
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