How many gph for a 75-gallon reef tank?

Mixed reef target: 75 × 6 = 450 gph at the display. With typical 4 ft of head and 2 elbows, you need a pump rated 800–1000 gph at zero head. Sicce Syncra 4.0 (951 gph) or Vectra S2 hit the target.

What's the right turnover for an SPS-dominant tank?

8–10× display volume per hour through the return. That's separate from in-tank flow (Vortech MP40s, Gyres) which can deliver another 10–20× turnover. The return pump exchanges water with the sump; the powerheads circulate it within the display.

How much flow does my Bean Animal overflow handle?

About 1500 gph for a 1.5-inch primary plus a 1-inch backup, quietly. The Bean Animal's third 'emergency' standpipe handles the overflow case. Most builders run 800–1000 gph through a Bean Animal to keep noise low.

Should I get an AC or DC return pump?

DC for almost every reef tank: controllable, energy-efficient, flatter head-loss curve, generally quieter. AC pumps (Eheim, Mag-Drive) are cheaper upfront and run reliably for years but lack speed control. Eheim 1262 is still the workhorse if you want bulletproof.

How do I measure head height accurately?

Tape measure from the floor of your sump (where the pump sits) to the rim of your display tank. That's vertical head. Then count every 90° elbow on the return-side plumbing — each one costs roughly 0.5 ft equivalent head.

Calculator

Return Pump Flow Rate Calculator

Return pump sizing is the calculation everyone gets wrong by either undersizing (the display starts looking still) or oversizing (the overflow can't keep up and the sump siphons dry). The math is two numbers — target turnover at the display × head-loss factor — and the right answer is usually a DC pump tuned to deliver the display number with 30% headroom.

Return pump flow rate

Display volume (US gal)

Tank style

Softie/FOWLR: 4×. Mixed: 6×. SPS-dominant: 8× turnover.

Vertical head (ft)

Floor of sump to rim of display. 3–5 ft is typical.

Number of 90° elbows

Count plumbing elbows on the return line. Each adds ~0.5 ft of head.

Rated flow (at 0 head)

900gph

Buy a pump rated at or above this number.

Flow at display

450gph

Turnover target

6×/h

Effective head

5ft (loss 50%)

Head-loss model is a 10% per ft linear approximation tuned to typical DC pump curves (Sicce Syncra, Vectra L1, Reef Octopus VarioS). Real curves differ — check the pump's published flow-vs-head chart before buying.

How this is calculated

required_flow_at_display = display_gal × turnover_per_h
effective_head           = vertical_ft + 0.5 × number_of_90s
flow_loss_pct            = effective_head × 10   // capped at 80%
rated_flow_at_0_head     = required_flow_at_display / (1 - flow_loss_pct/100)

Why rated flow ≠ flow at display

Pump manufacturers publish a single number — the rated maximum flow at zero head. Real plumbing has 3–6 feet of vertical lift, two to four 90° elbows, a bulkhead fitting, valves, and maybe a manifold. Each adds friction. The result: rated 1500 gph delivers 600–900 gph at the display in a typical sump.

The 10% per foot rule of thumb works for most AC and DC pumps in the hobby band (300–3000 gph rated). It's tuned against published flow curves for Sicce Syncra, Ecotech Vectra, and Reef Octopus VarioS. DC pumps have flatter curves (less loss at high head) than AC pumps; always check the published curve before buying.

Why not just run it harder

Higher return pump flow doesn't equal more circulation in the display. The display gets its flow from powerheads (Tunze, Vortech MP40, Maxspect Gyre) — the return pump just exchanges water between sump and display. Pushing the return harder buys you faster water exchange with the sump (more skimmer contact, faster nutrient export) but stops being useful past 10× turnover. It also strains your overflow.

Two operational caps:

Your overflow rating — a Bean Animal triple-drain handles 1500 gph; a Herbie up to 1000 gph; a single-line standpipe much less. Don't plumb more flow than the overflow can drain quietly.
Heat from the pump — most reef DC pumps add 50–200 W of waste heat to the water. Running flat-out 24/7 adds noticeable heater-substitute load. Throttle to 60–80% of rated as a normal operating point.

FAQ

How many gph for a 75-gallon reef tank?: Mixed reef target: 75 × 6 = 450 gph at the display. With typical 4 ft of head and 2 elbows, you need a pump rated 800–1000 gph at zero head. Sicce Syncra 4.0 (951 gph) or Vectra S2 hit the target.
What's the right turnover for an SPS-dominant tank?: 8–10× display volume per hour through the return. That's separate from in-tank flow (Vortech MP40s, Gyres) which can deliver another 10–20× turnover. The return pump exchanges water with the sump; the powerheads circulate it within the display.
How much flow does my Bean Animal overflow handle?: About 1500 gph for a 1.5-inch primary plus a 1-inch backup, quietly. The Bean Animal's third 'emergency' standpipe handles the overflow case. Most builders run 800–1000 gph through a Bean Animal to keep noise low.
Should I get an AC or DC return pump?: DC for almost every reef tank: controllable, energy-efficient, flatter head-loss curve, generally quieter. AC pumps (Eheim, Mag-Drive) are cheaper upfront and run reliably for years but lack speed control. Eheim 1262 is still the workhorse if you want bulletproof.
How do I measure head height accurately?: Tape measure from the floor of your sump (where the pump sits) to the rim of your display tank. That's vertical head. Then count every 90° elbow on the return-side plumbing — each one costs roughly 0.5 ft equivalent head.

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Sources & references

01
Bulk Reef Supply — Return Pump Sizing Guide
https://www.bulkreefsupply.com/content/52-weeks-of-reefing
02
Sicce Syncra Silent Pumps — performance curves
https://www.bulkreefsupply.com/sicce-syncra-silent-pumps.html
03
Ecotech Marine — Vectra DC pump series
https://ecotechmarine.com/products/vectra
04
Reef Octopus VarioS controllable DC pumps
https://www.bulkreefsupply.com/reef-octopus-varios-controllable-dc-pumps.html

Last reviewed 2026-05-25