🚀 go-pugleaf

The term "float switch" could describe a lot of things.  In 
connection with aquaria, it generally refers to a device which
senses water level, and when that level passes above or below
a particular set point, throws a switch to provide power to
something or to stop providing power.  They generally switch
regular 110V outlets so that you can plug in any device.  The
physical switch may directly toggle line power, or it may 
control a low voltage relay which in turn controls line power.

The kind I'm familiar with have a styrofoam float with a magnet
imbedded in it, and a reed switch which throws when the magnet
is next to it.  By turning the float around, you can have it
either provide power when the water level is high, or cut off
power.

The ones sold especially for aquariums are often quite expensive.
I made one myself which has worked fine for over a year now.  The
key piece is a float switch from W.W.Grainger (a nation-wide chain
of industrial suppliers), part number 2A554 for $10.50.  I'm fairly
certain it's properly rated to control power heads, although some-
one has questioned this and I keep forgetting to double-check the
specs.  It is saltwater safe.  To this switch I add an aquarium
airline suction cup to hold it in place in the sump, and connect
the wires to half of a "switched outlet".  This is a device you can
get where extension cords are sold which has a switch at one end of
a long cord and a plug/outlet combination at the other end.  I cut
the wire and replace the switch with the float switch, and voila!
The float switch controls the outlet.
					-Mark