Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Use a fountain pump in the tank and run the tubing up the intake tube of the HOB.
HOB or canister will not pick up water when the water in the tank is more than a few inches low. They are designed to work best when the tank is full.
Alternate: If you never will want to fill the tank again cut a hole through the glass just above the water level for the HOB.
Alternate: Get an internal filter. Yea, it takes up room that the turtles could use. Duetto and other companies make them.