Reef Tank Sump Setup: Plumbing, Gear and Order

A reef tank sump is the part of the system nobody sees and almost everybody eventually regrets rushing. It decides how quiet the display is, how steady the water level stays, whether a power cut reaches the floor, and how much equipment has to sit inside the tank. We plumb these on installs across Chicago and the suburbs, and the same handful of decisions separate a sump that runs untouched for years from one that gets rebuilt in month three. Nearly all of them are made before any water goes in.

What a reef tank sump does and how big it needs to be

Four jobs, in rough order of importance. It adds water volume, which slows every swing in temperature, salinity and nutrients. It gives the overflow somewhere to send the protein-rich surface film. It hides the skimmer, heaters, reactors and dosing lines. If you are still working out the sequence of the whole project, our reef tank beginners guide covers that ground.

The fourth job is the one people size for last and should size for first: holding the water that drains out of the display and the plumbing when the return pump stops. A fifth to a third of the display volume is a comfortable target, and bigger is better right up to the point where it will not fit.

The constraint is rarely the stand's interior width. It is the door opening, so measure the clear opening and the diagonal you can tilt a tank through before ordering anything. Check that you can still reach the far corners with the sump in place, because a sump you cannot reach into stops getting serviced properly.

Chamber order runs drain, skimmer, refugium, then return

Water should meet the equipment in the order that makes each piece work. The drain lines enter the first chamber into a filter sock, a roller mat or a block of mechanical media, and the protein skimmer belongs in that same first chamber where dissolved organics are highest. Feeding a skimmer from the return chamber means it processes water that has already passed everything else, which is backwards and measurably less effective.

The middle chamber holds the optional equipment. A refugium of chaeto under a small light exports nitrate and phosphate and gives copepods somewhere to breed. Reactors for carbon or granular ferric oxide, a UV sterilizer, or simply open space for a heater all work here. Flow through this section should be gentler than the first, which is why refugium designs usually sit behind a taller baffle and spill over the top.

The last chamber holds the return pump, and it is the only one whose water level is allowed to move. Everything upstream sits behind fixed-height baffles, so evaporation shows up here alone and the skimmer keeps a constant water depth. Put a heater in this chamber too if there is room, since the pump keeps it in moving water and covered.

Baffles and bubble traps set how quietly a reef tank sump runs

A baffle is a pane of glass or acrylic siliconed across the sump, and its height fixes the water level in the chamber behind it. Two baffles set an inch to an inch and a half apart, the first running from the floor to a fixed height and the second hanging from above with a gap beneath, make the classic over-under bubble trap. Water is forced down, then up, and microbubbles surface instead of reaching the return pump.

Three panes work better than two if the length is available, and the spacing matters more than the count. Traps that are too tight accelerate the water and push bubbles straight through. Use structural silicone rather than a bathroom product, and fit a removable filter sock holder, because everything in a sump has to be serviceable with the tank running.

Skimmer depth is the detail that catches people out. Most skimmers specify a water depth range, commonly somewhere between six and nine inches, and an inch too deep or too shallow makes them foam erratically and refuse to tune. Set the first chamber's baffle height to the depth your skimmer actually asks for rather than to a round number, and confirm it before the silicone cures.

Durso, Herbie and BeanAnimal drains are not interchangeable

A Durso is the simplest of the three: one standpipe in the overflow, vented at the top with a small hole, running partly full. It needs no tuning and costs almost nothing, and it gurgles. Flow through it shifts as the vent clogs, so the overflow water level wanders. In a basement fish room that is fine; under a television it is not.

A Herbie uses two lines. The main drain runs as a full siphon, throttled with a gate valve until it carries exactly what the return pump delivers, while a second standpipe stands dry as an emergency. A full siphon is silent because there is no air in the pipe. The trade is that it needs tuning, and the emergency line must be sized for full flow and checked at every service visit.

A BeanAnimal adds a third line. Siphon, open channel and emergency together let the open channel absorb small changes in flow, so the system self-corrects instead of depending on a perfect valve setting. It is the quietest and most forgiving of the three, and it is what we specify on most display builds. Our notes on fish room plumbing and electrical work cover what changes when the sump lives in its own room.

Return pump sizing and the head loss everyone underestimates

Turnover through the sump is not the same as flow inside the display. Powerheads and gyres handle circulation for the corals; the return only has to move enough water for skimming, gas exchange and heat distribution. Something around five to ten times the display volume per hour is plenty. Pushing much more than that makes the first chamber turbulent and drives bubbles past the traps.

Head loss is where catalog numbers stop meaning much. A pump rated at a given output with no head loses a large share of it climbing from the sump surface to the return nozzles, then passing through elbows, a union, a valve and a length of flexible hose. Count the vertical rise first, add roughly a foot of equivalent rise per ninety-degree elbow, and read the answer off the pump curve.

Two habits save trouble later. Use a variable-speed DC pump so flow can be trimmed after the drain is tuned rather than throttled with a valve, and drill a small siphon-break hole in the return line just below the display's water surface so the tank stops draining a few inches down. Never rely on a check valve alone, because they foul with coralline and a stuck one is a flood.

Top-off placement and the order to assemble everything

The top-off sensor belongs in the return chamber, since that is the only place the level moves in a well-baffled sump. Mount it on a bracket away from the pump's turbulence, and use two devices rather than one: an optical or float sensor to switch the pump, and a second high-level float wired to cut power if the first sticks. Snails and coralline foul optical sensors, so wiping them is routine.

Size the reservoir for a few days of evaporation rather than a few weeks. A large drum of fresh water sitting above a reef tank is a salinity accident waiting on a failed valve, and a smaller container keeps that failure survivable. Fill it with reverse osmosis or deionized water only, and anchor the tubing so it cannot fall out and pump air into the sump.

Assembly order matters more than people expect, because most of the mistakes above can only be corrected while a reef tank sump is dry and empty:

1. Dry-fit the sump in the stand and confirm you can still reach the return chamber and lift a sock out.

2. Set the drain plumbing, emergency line included, and support the pipe so nothing hangs off the bulkheads.

3. Set baffle heights to the skimmer's specified water depth, then silicone and let it cure fully.

4. Plumb the return with unions either side of the pump, and drill the siphon-break hole before the first fill.

5. Fill with fresh water, run it for a day, tune the drain, then cut the power and confirm the drain-down fits.

6. Only then add salt, set salinity, and commission the top-off last so it is not chasing a moving target.

Key takeaways

• Size for drain-down volume first, total volume second, and measure the stand's door opening before buying.

• Skimmer in the first chamber, optional media in the middle, return pump and top-off sensor in the last.

• Baffle heights set the skimmer's water depth, so build to its spec sheet rather than to a round number.

• A BeanAnimal drain is quietest and most forgiving, a Herbie is silent but needs tuning, and a Durso gurgles.

• Size the return pump off its head-loss curve, not its headline rating, and drill a siphon break.

Frequently asked questions

How big should a reef tank sump be?

Aim for a fifth to a third of the display volume, then check two limits. It has to fit through the stand's door opening, and it has to hold everything that drains out of the tank and the return line during a power cut, with the running level marked below that point.

Can I run a reef tank without a sump?

Yes, with an all-in-one tank or hang-on equipment, and plenty of nano reefs do well that way. What you give up is water volume, a quiet home for a full-size skimmer and heaters, and steady surface skimming. Below roughly forty gallons the trade is reasonable, and above that a sump usually earns its place.

Why is my sump throwing microbubbles into the display?

Usually one of three causes. The skimmer is over-foaming or still breaking in, the bubble trap spacing is too tight and water is moving through it too fast, or the return pump is drawing air from a loose fitting or a low water level.

Work with Marine Concepts Inc

If you would rather not spend a weekend under a stand with a tube of silicone, our aquarium installation service covers the sump, the drain plumbing and the leak testing as part of the build, and pumps, skimmers, plumbing parts and media are available for same-day pickup at Marine Concept Supply in Wheeling, IL.