Good flow keeps a reef tank stable. It moves oxygen, heat, and food. Smart powerhead placement also prevents dead spots and algae mats.
Start with goals and baseline flow
Pick a flow target before you move equipment. Most mixed reefs do well at 20–40x tank volume per hour. SPS-heavy tanks often run 40–70x. Soft coral tanks may prefer 15–30x.
Use your return pump as background flow only. Build most movement with powerheads. Aim for wide, turbulent flow instead of a hard jet. This reduces tissue damage and sand storms.
Watch how food and detritus travel. Add a pinch of flakes and observe for 30 seconds. If it drops straight down, you have a dead zone. If it blasts into the sand, your angle is too low.
Map your rockwork and coral zones. SPS like strong, changing flow at the top. LPS prefer indirect flow that makes tentacles sway. Use your aquascape as a flow baffle, not a wall.
- Mixed reef starting point: 2 powerheads at 30–50% each
- Keep outlets 2–4 inches below the surface for gas exchange
- Re-check flow after each new coral or rock change
Placement patterns that work in real tanks
The simplest pattern is opposing sides. Place one powerhead high on the left. Place the other high on the right. Angle both slightly up to ripple the surface.
For longer tanks, try a “gyre” loop. Put one pump high on one end, aimed across the top. Put the second low on the same end, aimed back along the bottom. This keeps detritus suspended for capture.
In cube tanks, crossflow is often better. Put pumps on adjacent sides, not opposite. Aim them to collide in the center. The collision creates random turbulence without a sand blast.
Use your overflow as a tool. Aim flow so particles drift toward the weir. A filter sock or roller then removes waste. See reef tank filtration basics for matching flow to export.
- Keep pumps 3–6 inches from rock to avoid “laser” channels
- Aim jets at glass first to diffuse flow in small tanks
- Leave a calm corner for LPS and feeding stations
Fine-tuning, troubleshooting, and common mistakes
Use modes that vary speed. Pulse or random modes reduce laminar flow. Start with a 1–2 second pulse and adjust. Short pulses can kick up sand in shallow tanks.
Sand storms usually mean the pump is too low or too strong. Raise it 1–2 inches and angle it up. If needed, reduce output by 10–20%. Coarser sand also resists shifting.
Detritus piles behind rock are very common. Add a small “helper” pump low in the back. Aim it along the back wall. Run it on a timer for 10 minutes, twice daily.
Watch corals for flow stress. SPS tips can pale under constant blast. LPS can retract if hit directly. If you see tissue peeling, check alkalinity and flow together. Use reef tank water parameters as your stability checklist.
- Clean wet sides every 4–6 weeks to keep output consistent
- Keep cords in drip loops and test GFCI outlets monthly
- Quarantine new frags to avoid pests that hate strong flow
Once placement looks good, validate it during feeding. Target feed LPS with pumps in feed mode for 5–10 minutes. Then restore flow to prevent waste settling. For more on feeding with flow, see coral feeding guide.
Powerhead placement is never “set and forget.” Corals grow and block flow. Re-test monthly with food or fine sand in a cup. Small changes keep your tank clean and your corals extended.
Sources: Ecotech Marine VorTech user guides; Bulk Reef Supply flow and circulation articles; Delbeek & Sprung, The Reef Aquarium (flow and husbandry sections).
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