I know this is a stupid question, but I just don't know: Are water feature
pumps, like those installed in small fountains, waterfalls or ponds,
supposed to be left running all the time? I'm assuming they are, in order
to prevent stagnation and the development of algae. If so, are they much of
an impact on one's electric bill?

Happy Holidays to all!

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Better a bleeding heart than no heart at all.