How much flow does a reef tank need?
Calculate a practical flow target for soft coral, LPS, mixed reef, and SPS systems without confusing return-pump turnover for coral flow.
Most reefs need more internal flow than beginners expect. ReefCrafter uses 10x display gallons as the minimum for soft/LPS systems, 20x for mixed reefs, and 40x for SPS-dominant systems, counted primarily from powerheads or wavemakers. Return pumps help filtration turnover, but they are not a substitute for broad, random display flow.
Quick check
- 1Pick the reef goal: soft/LPS, mixed reef, or SPS dominant.
- 2Multiply display gallons by 10, 20, or 40.
- 3Add the max GPH from powerheads or wavemakers.
- 4Use return-pump flow as a bonus, not the main source of coral flow.
- 5Plan for two controllable sources on longer tanks to reduce dead spots.
ReefCrafter math
Turnover is a starting point, not the whole answer
A single GPH number does not tell you whether detritus is staying suspended, whether coral tissue is getting blasted, or whether the back side of the rockwork is stagnant. ReefCrafter uses turnover as the first safety check because it catches obviously underpowered builds before they become algae and detritus problems.
Why return pumps do not count the same way
A return pump moves water through the sump, plumbing, and overflow. After head loss, elbows, valves, and nozzles, the display usually sees much less useful movement than the box rating suggests. Powerheads and gyres are better tools for coral-facing flow because they can be placed where the dead spots actually are.
What good flow looks like
Healthy reef flow is broad, changing, and indirect. You want food and waste moving without sandstorms or coral tissue peeling back. A lower total GPH with two well-placed controllable pumps can beat a higher number from one harsh jet.
- Soft corals: gentle to moderate movement with no direct blasting.
- LPS: enough movement to keep tissue clean without whipping flesh.
- Mixed reefs: stronger top and mid-level flow with calmer lower zones.
- SPS: high, chaotic movement across the upper rockwork.
Common mistakes
- Counting return-pump box GPH as if it is display flow.
- Using one strong pump instead of two gentler, opposing sources.
- Pointing a narrow jet directly at LPS tissue.
- Ignoring rockwork that blocks the back half of the tank.
- Buying fixed-speed pumps when the coral plan may change.
Buying/spec checklist
- Combined powerhead GPH meets the ReefCrafter minimum for your reef goal.
- Pump strength is controllable or has useful modes.
- Mounts fit your glass thickness.
- Placement can reach behind and around the rockwork.
- The tank can run lower flow at night or during feeding if needed.
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FAQ
Is 10x turnover enough for a reef tank?
It can be enough for soft coral or low-energy LPS systems, but it is not enough for most mixed reefs or SPS-dominant builds. ReefCrafter treats 10x as a floor, not a premium target.
Can I have too much flow?
Yes. Too much direct flow can strip tissue, keep sand suspended, and make fish avoid parts of the tank. The goal is broad, chaotic movement, not maximum GPH at all costs.
Do AIO tanks always need an extra powerhead?
No. Many AIO tanks already create enough movement for soft coral goals, especially small systems. ReefCrafter flags AIO powerheads as an advisory because extra display flow can be unnecessary or awkward in tight tanks.