Return pump

Pump that transports water from the sump to the main aquarium. Correct sizing is essential for the circulation and functioning of the system.

Detailed explanation

The return pump is the hydraulic heart of a sump system. It takes water from the sump after it has passed through the skimmer, refugium and other filtration compartments, and sends it back to the main aquarium.

The flow rate of the pump must be calculated taking into account the head, i.e. the vertical distance between the water level in the sump and the discharge into the aquarium, plus the pressure losses due to bends and length of the pipes. Every metre of head reduces the effective flow rate.

The general rule says that the effective flow rate of the return pump should be 5-10 times the volume of the aquarium per hour. For a 300-litre aquarium you need a pump with an effective flow rate of 1500-3000 l/h. Attention: the flow rate declared by the manufacturer is that of zero head. At 1.5 metres head a 5000 l/h pump can drop to 2000.

DC (direct current) pumps are quiet, adjustable in flow rate and consume less energy. AC (alternating current) pumps are cheaper and more robust but noisy and not adjustable.

The most reliable brands are Sicce, Eheim, Jebao, Reef Octopus and Neptune Systems (COR). The Sicce SDC are very popular in Italy for their good quality/price ratio.

The delivery pipe must have an adequate diameter (typically 20-25mm). A hose that is too narrow creates friction and reduces flow. Curves at 90 degrees should be minimized.

The pump must be positioned so that it does not suck in air when the sump level drops. An inlet guard (sponge prefilter) prevents debris from clogging the impeller.

Coralia Lab offers a return pump calculator that estimates actual flow rate based on head and pipe diameter.

How it is measured

The actual flow rate is calculated with the pump performance curve (provided by the manufacturer) based on the total head of the system.

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