A swamp cooler is the explantion I offered him -- in fact, his waterfall
runs off a swamp cooler pump! His filter, as I understand it, is
separate. I've slowed down my feeding, but my fish are still interested
on warmer days. I am feeding pellets that are labeled for fall and easy
to digest. Most days the water is over 50 degrees but we've had a few
dips under.

Thanks!

Gabrielle

RichToyBox wrote:

Evaporation causes cooling that is faster than the direct conduction of heat
from the pond to the air. In southern Arizona, many years ago, we used
swamp coolers for our air conditioning. The water falling over a waterfall,
or tumbling down a stream, or being shot into the air for a fountain, has a
higher surface area than the pond, and therefore will have higher
evaporations than the pond alone. The pond will be cooler with the
fountain, stream or waterfall running than without. If the pond temperature
is above 50 degrees, then the fish should be being fed, and the filter needs
to be running if the fish are feeding. The filter should not be cycled on
and off. It will go anaerobic during the shutdown, producing hydrogen
sulfide gas which is very toxic to the fish, and the filter bacteria will
die back such that the nitrogen cycle is not taken care of. I know people
up north turn off the filter for the winter, and that is because of the
potential of freezing pipes in a power outage, or ice buildup at the
waterfall that can cause the water to be diverted from the pond. I
definitely would not turn off the filter unless the pond temperature falls
below 40 degrees, which is the temperature that the filter bacteria are
reported to die off.