Re: Python vs Meridian Auto Water Changer

The two products are quite different, and have different uses.

The Python is meant to be an easy, spill-free way for you to go about
changing water and "vacuuming" the gravel.  You hook it up to the faucet,
turn the water on, and adjust a valve to create a "suction" (by Venturi
action) to drain water from the tank.  A large Hydroclean-type tube can be
used to whirl the gravel and to clean it.  When the tank is  drained enough,
you flip the valve again and fill the tank.  The heart of the system is the
Venturi / valve combination, which is very similar to one that might be
purchased to drain and fill waterbeds.  It works very well, but the
gravel-cleaning part obviously shouldn't be used in a heavily planted aquarium.

The Automatic Water Changer also hooks up to the sink and the tank but is
meant to be simply turned on for a brief time daily to exchange some old
water for new.  It sprays new (cold) water in at the top, and simultaneously
draws water, also from the top (to prevent risk of siphoning tank dry while
unattended.  It's not meant to remove any debris; in fact, floating debris
could plug the outflow and cause the tank to overflow.  It also cannot be
run for too long a period in most circumstances or the cold water could
chill the tank (it has to run at a high flow rate for the outflow mechanism
to work).