Return Pump Sizing Guide: How to Pick the Right One for Your Sump

The Pump That Makes Your Sump Actually Work

A return pump pushes water from the sump back into the display tank. Get it right and everything flows beautifully. Get it wrong and the sump either overflows or trickles water back at a rate that defeats the whole purpose.

The Basic Maths

The general recommendation is a turnover of 5–10 times per hour. So a 200-litre display wants a return pump pushing 1,000–2,000 LPH back to the tank.

The key detail many reefers miss: that flow rate needs to be measured at the actual head height, not the pump's rated maximum. Every pump loses flow as it pushes water upward against gravity.

Understanding Head Pressure

Head pressure is the vertical distance from pump to display, plus losses from bends and fittings:

• Every metre of vertical height costs significant flow — check the pump's flow curve chart
• Every 90-degree elbow adds roughly 30cm equivalent
• Every metre of horizontal pipe adds roughly 10cm equivalent

So a sump 1 metre below the display with two 90-degree elbows gives roughly 1.6 metres effective head. Look at the pump's flow-at-head chart to find the actual flow at that height.

Popular Options in the UK

Budget (£30–80):

• Jebao DCP series — The DCP-3500 and DCP-5000 are popular choices. Controllable flow, quiet, and strong value
• Jebao DCS series — Similar performance, slightly different form factor

Mid-range (£80–180):

• Sicce Syncra SDC — Italian-made, very reliable. Good flow curves and quiet operation
• Eheim CompactON — Not DC-controllable on basic models, but extremely reliable

Premium (£180–400+):

• EcoTech Vectra S2 / M2 — App-controlled, integrates with the Mobius ecosystem. The S2 handles tanks up to about 300L, the M2 goes bigger
• Royal Exclusiv Red Dragon — Whisper-quiet, excellent build quality. A favourite for high-end builds

Sizing Tips

• Slightly oversized is better than undersized. A DC pump running at 70% is quieter and more efficient than a smaller pump at full blast
• Match the overflow. A pump rated at 3,000 LPH is pointless if the overflow only handles 2,000 LPH
• Keep a spare. A dead return pump means the sump, skimmer, and display all stagnate. Even a cheap backup pump is smart insurance

Buying Used

Return pumps are simple devices. If the impeller spins and the seals don't leak, a used pump works identically to a new one. Browse pumps from UK sellers — quality return pumps regularly appear at a fraction of the new price.

What return pump are you running and how did you size it? Always useful to hear real-world flow rates versus manufacturer claims.