Choosing the Right Powerhead Size for Your Tank

Winter in Brisbane means the AC and heaters are both working overtime, and a lot of reef keepers use the cooler months to finally sort out flow instead of just topping up evaporation. If you bought a powerhead based on tank length alone, there is a decent chance your corals are either getting flattened or sitting in a dead zone behind the rockwork. Sizing flow properly takes about five minutes with a calculator and a tape measure, so there is no excuse to keep guessing.

What you need:

• Tank volume in litres (not the display size on the box, the actual water volume)
• A powerhead or wavemaker rated in litres per hour (LPH)
• Tape measure or a rough idea of rock structure density
• Five minutes and a calculator app

The turnover number that actually matters

Most reef tanks want total pump turnover somewhere between 20 and 40 times the tank volume per hour, combined across return pump and powerheads. SPS dominant tanks sit at the higher end, softies and LPS tanks are happier lower. A 200 litre reef tank at 30x turnover needs roughly 6000 LPH split across your equipment, not from one unit.

Step by step

1. Work out your net water volume in litres. A 4ft tank often holds less than the box says once rock and sand displacement is factored in.
2. Decide your turnover target. Mixed reef, aim for 25 to 30x. Heavy SPS, aim for 35 to 40x.
3. Multiply volume by target turnover to get total LPH needed.
4. Subtract what your return pump already provides.
5. Split the remainder across two or three powerheads rather than one big unit blasting from a single point.

Sizing real units

An Eheim CompactOn 600 pushes 600 LPH and suits nano tanks or as a supplementary flow point in a tank under 100 litres, priced around 88 AUD. Step up to something like the VorTech line in the Prices are accurate at the time of publishing and are subject to change. Check the product page for the current price before buying.