Setup
How much flow does a reef tank need?
beginner
4 min read
FlowEquipment
When: While setting up circulation, before cycling starts
Short answer: Aim for roughly 7-10x your total tank volume per hour of turnover from your return/circulation pump, delivered as random, variable flow from more than one point rather than a single strong jet — the goal is no stagnant "dead spots" where detritus and cyanobacteria build up, not hitting an exact number.
The details
The corpus's specific, sourced turnover figure is 7-10x tank volume per hour for a return pump. Beyond that baseline, the quality of flow matters as much as the quantity:
- Random/variable flow beats one constant direction. Corals evolved in chaotic wave surge, not a laminar jet — gyre-style pumps and alternating wavemakers are specifically called out for eliminating dead spots that a single fixed powerhead leaves behind.
- DC pumps are the modern default — controllable, quieter, more efficient, and some offer battery backup so flow (and gas exchange) continues through a power cut.
- Rockwork blocks flow over time. Overgrown coral colonies choke flow paths; regular fragging/trimming is part of maintaining circulation, not just coral management.
- Total combined turnover across every pump in a full reef (return + all powerheads together) isn't given a single universal number in this corpus — treat any such combined figure you see elsewhere as unverified; what's sourced here is the 7-10x return-pump baseline plus the qualitative goal of eliminating dead spots.
The numbers
| Parameter | Target |
|---|---|
| Return/circulation pump turnover | 7-10x tank volume per hour |
| Flow style | Random/variable, multiple points |
| Dead spots | None — reposition pumps until there aren't any |
Common mistakes
- One powerhead aimed straight across the tank. Creates a strong dead zone directly behind rockwork.
- Never repositioning flow as the aquascape fills in with coral. What worked on an empty tank stops working once rock is covered.
- Confusing return-pump turnover with total in-tank flow. Powerheads add flow on top of the return; there's no single sourced combined target here, so don't chase an invented number.
When to worry
- Normal: Mild sway in soft corals and gentle sand ripple.
- Worry: Visible detritus piling in a corner or cyanobacteria forming in a low-flow pocket — that's a flow/dead-spot problem; see the-ugly-phase-is-normal once the tank is running.
What's next
With flow sorted, choose your rock in live-rock-vs-dry-rock.
Target parameters
turnover_target7-10x total tank volume per hour (return/circulation pump)
flow_stylerandom/variable, from more than one point
placement_goalno stagnant dead spots behind rockwork
Red flags — act now
- Detritus visibly piling in one corner
- Cyanobacteria forming in a low-flow pocket
Sources
- Reef Knowledge Base — Flow & Pumps
- Reef Knowledge Base — Flow / Pumps / Wavemakers (batch detail)
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