I'm not familiar with any pumps designed for aquariums that can handle 20 ft of head pressure. Only thing that comes to mind would be a well pump, and that probly isn't a very good idea.
Aquarium Water Pump Head Pressure and Pump Performance
As the head pressure increases the gph
Each 90-degree bend in the plumbing will add about one foot of head due to friction. Each 45-degree bend will add 1/2 foot head pressure. This includes any bends in filters, chillers and uv
As a result of friction, each 10-foot horizontal run of pipe will add a foot of head pressure.
In an open system (a system using a sump), each foot of vertical distance from the intake of the pump to the return into the aquarium will add one foot of head pressure. The vertical distance in a closed system does not affect head pressure. A closed system is one where the pump draws water directly from the aquarium and returns water directly to the aquarium.