Free tool
Reef Flow Calculator
Flow is the most under-measured parameter in reef keeping. Tell us your tank volume and what you keep, and we will translate it into honest GPH numbers: how much your return pump should move, how much your wavemakers should add, and which equipment class fits the result.
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Reference
Turnover targets by coral type
Total turnover is everything moving water in the display: return pump plus wavemakers. The return alone should run 5 to 10x tank volume per hour; wavemakers supply the rest. This table works without any of the controls above.
| What you keep | Total turnover target | Why |
|---|---|---|
| Soft coral / FOWLR | 10 to 20x tank volume per hour | Softies and fish-only systems need gentle, complete circulation. Enough to keep detritus suspended, not enough to fold leather corals over. |
| LPS and mixed reef | 20 to 30x tank volume per hour | LPS polyps feed in moderate, varied flow. Strong enough to keep the rockwork clean, indirect enough that fleshy polyps are not torn. |
| SPS-dominant | 30 to 50x tank volume per hour | Acropora and other SPS need high randomized flow across every branch to shed mucus, deliver food, and prevent dead spots inside dense colonies. |
How it works
How this tool works
Flow in a reef tank is two separate jobs, and the calculator splits them. The return pump moves water through the sump for filtration and skimming, and it is sized as a modest multiple of tank volume per hour after head loss. Wavemakers create the in-tank turbulence corals need to feed and shed waste, and that requirement changes with what you keep: soft corals and fish-only tanks want gentle, varied flow, LPS and mixed reefs want moderate, and SPS-dominant tanks want strong, chaotic flow that would tear soft corals off the rock.
You enter volume and coral type, and the tool returns a total turnover target, a return-pump range and the wavemaker flow that makes up the difference. The numbers are derived from widely used turnover ranges for each coral group, stated conservatively so a slightly undersized pump errs toward calm rather than sandstorms.
Reading the result
How to read your result
The return pump range is the smaller number and it is a rated flow, so account for head height and plumbing losses; a pump loses a large share of its rated flow lifting water four feet through elbows. Buy toward the top of the range or choose a controllable DC pump you can dial back.
The wavemaker number is total in-tank flow, and it is usually split across two units on opposite ends so the flow is random rather than a single stream. Controllable pumps let you start at half the figure and ramp up as corals settle.
FAQ
Questions people ask
What turnover does a reef tank need?+
Roughly five to ten times tank volume per hour through the sump, and in-tank flow of 10 to 20 times for soft coral and LPS tanks, 30 to 50 times or more for SPS. The calculator applies the range for your coral type.
Can I have too much flow?+
Yes. Sand storms, corals that stay closed, and fish hiding constantly are all signs. Directing pumps toward the glass or up at the surface, or lowering a controllable pump's power, fixes most cases without new hardware.
Why does head height matter for the return pump?+
Every foot the pump has to lift water, and every elbow in the plumbing, reduces its actual output. A pump rated at 1,000 GPH may deliver 600 at four feet of head. Check the pump's flow curve, not its headline number.
Do I need a gyre or a propeller pump?+
Either works. Gyre pumps produce broad, sheet-like flow that suits long tanks; propeller wavemakers produce a wider cone that suits cubes and mixed reefs. Two smaller pumps beat one large one for randomness.