"Elaine T" wrote in message
om...
George wrote:
"Reel McKoi" wrote in message
...

"ba5416" wrote in message
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The ice came off the pond a week or so ago. Found several fish floating on
the surface and several on the bottom. Pond is about a 1000 ga, 4ft deep

at

the deep end. Pond has been in place for 4 years now with no problems. I
leave the pump running 24/7/365, turn the fountain off and leave the
waterfall run to keep things open.
Did the water quality tests once I found the dead fish. Everything was

OK.

$ You didn't allow the fish to find the "warm spots" at the bottom of the
pond and rest for the winter. The current and cold probably killed them.
Just about everyone in a cold climate turns the waterfalls etc off to allow
this natural rest period - and so that the water can do it's natural
conversion (cold at the top, warmer and still at the bottom.)


I see that you flunked thermodynamics. Cold water sinks. Warm water rises.
I see you fluked chemistry. ;-) Water is at its absolute highest density at
4 degrees C, above freezing. Because of this, interesting thermal
stratifications can occur in cold, still water.


I was waiting for someone to bring this issue up. It was discussed at length
last fall. In an effort to see how this affects shallow garden ponds, I
conducted a little experiment, measuring the water temperature at the surface,
and comparing it with water at the bottom (45").

Starting with autumn, let's see how the pond changed into the winter. The water
at the surface started out in October at 42°F. The first frost and cold wind
lowered the surface layer and it sank, while the warm water rose and replaced it
and was chilled in turn. This circulation process continued until all the water
reached 39.2°F, at this temperature water is at its heaviest. Normally, any
cooling beyond 39.2°F does not sink, instead forms a thin layer at the surface
because of the local geothermal gradient, which will warm any water that is
below the frost line. However, with shallow ponds, the cold water can continue
to sink (especially if the pond is not dug below the frost line), and cause the
pond to continue to cool, and if this process continues, the pond can freeze
completely to the bottom. When the weather is cold enough the surface freezes
at (32°F). Freezing at the surface helps to stop the circulation, and the warm
water will stay at and below the frost line. Interestingly, when my pond
started to freeze (it only froze slightly on the very ends because I use a
de-icer), the fish didn't stay on the bottom, but hovered just below the ground
surface (my pond is 18" aboveground, and 27" below ground, so they hovered at
about 18-20" below the water surface). In other words, they stayed about a
third of the way down in the pond. Before the ice began to form, but while the
air temperature was still dropping, the water at the bottom continued to drop
until it reached a temperature of 34-35 degrees, at which time it stabilized
Which was about the same temperature as the water just below the surface (about
4 inches). It never dropped below this temperature range. When the temperature
was just above freezing, both the surface and the bottom water stayed around
34-36 degrees. The point is that unless a garden pond is dug well below the
frost line, you are not likely to see much of the stratification you normally
would see. This is why ponds that are not dug below the frost line can and do
freeze solid during a cold winter.