| Sump | Hidden tank below for gear & volume |
| Refugium | A protected zone to grow macroalgae/pods |
| Benefits | More volume, hidden equipment, export |
| Refugium Grows | Chaeto (nutrient export) + copepods |
| Golden Rule | More water volume = more stability |
Overview
A sump is simply a second tank plumbed below the display where you hide equipment (skimmer, heater, return pump) and gain water volume — and more volume means a more stable, forgiving system. A refugium is a section of that sump, lit and protected from fish, where you grow macroalgae like chaeto and cultivate copepods. Together they’re one of the best upgrades for water quality and stability.
What Each Does
The sump gets gear out of the display, adds volume, and gives a place to run filtration and top-off. The refugium is a natural filter: a ball of chaetomorpha algae consumes nitrate and phosphate as it grows (you harvest it to export nutrients), while the sheltered rock and algae breed copepods that feed your corals and fish — a boon for mandarins and other pod eaters.
Setting One Up
- n
- Water overflows from the display to the sump, passes through chambers (filter sock/skimmer, optional refugium, return), and is pumped back up.
- Light the refugium on a reverse or opposite schedule to the display and pack it with chaeto.
- Harvest (trim) the chaeto as it grows — that’s the nutrient export.
- Screen the refugium so fish can’t eat the copepods you’re trying to grow.
n
n
n
n
Common Mistakes
No overflow safety planning: siphons and return-pump backflow can flood — size for power-off water levels. Never harvesting chaeto: unharvested macroalgae stops exporting and can go sexual/crash — trim regularly. Skipping a screen: fish will happily eat the pod population a refugium exists to grow. Pairs with a skimmer for full filtration.
Related Guides
How to Lower Nitrates and Phosphates · Protein Skimmers: How They Work & How to Tune One