[laverda]

You do not need a pressure pump for a closed loop unless you are planning on using educators which require pressure. Pressure pumps are designed for situations where you need to pump water up in height and have head pressure. Flow pumps are for creating flow and will not pump up very high. The dart will pump up to 12 feet, but the flow at 12 feet will be just about zero. At zero feet of head pressure it will flow almost 3600 GPH. A closed loop should have zero head pressure as you are not pumping water up above the water level in the tank. You will have some static pressure due to resistance to flow in the tubing your using and any elbows and fittings. If designed properly this will be minimal. In other words use 1.5" or 2 " tubing and keep elbows and fittings to a minimum.