I asked about a setup like that at my LFS and I found out that you need an overflow device in the top tank if you put your sump underneath the main tank. Gravity will pull all the water out of the main tank into the sump and overflow it. The filter would have to be pulling water out of the sump at the exact same rate or it will be uneven and flood. The filter would have to pump at the rate it's sucking water up + the added gravity force.
A: The store is right. I had forgot about that but that is the same reason external pond filters have overflows.
Nov 24, 2009
This will work but I have reservations by: Bill Brown
My only concern is the distance from the water in the sump to the top of filter. What you really have here are two aquariums, one without fish. I would be concerned about losing siphon (prime)in the sump which would allow the motor to run dry and damage the motor. Maybe someone else will have an idea also.
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