How many chambers should a sump have?

Three is common: a drain / mechanical chamber for filter wool and the protein skimmer, a biological chamber for media, and a return chamber for the pump and heater. More chambers are easier to fine-tune, but each chamber should be a whole 20mm multiple in clear width, or the water level will swing too much.

How large does the drain pipe need to be?

Estimating on gravity flow, each 25mm of internal diameter carries about 900 L/h. For a 350L system at 6× turnover, that is 2100 L/h and needs about 58mm of internal diameter, so take a standard 60mm; with a dual drain you could use 32mm on each.

Will a power outage flood the floor?

Everything above the water level in the main tank overflow box drains back down under gravity. The smaller the overflow box and the lower the pipe intake, the less comes back. Always leave at least 20% of the sump as buffer volume, and make sure the return chamber cannot be pumped dry and burn out.

Why does the return chamber water level drop?

Evaporation and clogged filter wool both lower the water level in the return chamber, while the other chambers stay put because their level is set by the baffles. So the return chamber needs allowance for evaporation, or an auto top-off.

How do I set baffle heights in a sump?

An underflow baffle (water passes underneath) sets the minimum water level in that chamber; an overflow baffle (water spills over the top) sets the maximum water level in the chamber upstream. Stepping them down progressively reduces bubbles, and the last overflow baffle sets the running water level in the return chamber.

D-02

Sump Design

What matters in a sump system is not how big the sump is, but that the drain keeps up with the return pump and that a power outage does not flood the floor. Those two are set by the drain pipe diameter and the sump buffer volume respectively.

Size a sump drain pipe by turnover flow: each 25mm of internal diameter carries roughly 900 L/h under gravity.

Units

Input parameters

Main tank and pump

Total system volumeUS gal

Used to recommend turnover flow at 6× per hour

Turnover flow (0 = auto)GPH

Drain pipe sized for the current 555 GPH

Main tank dimensions

Main tank lengthin

Main tank depthin

Main tank heightin

Stand heightin

Sump dimensions

Sump lengthin

Sump depthin

Sump heightin

Must not exceed the stand clearance, or it hits the countertop

Number of bafflespcs

4 chambers

Total system volume

Total system volume: 103.8 US gal
Sump water volume: 25.5 US gal
Recommended turnover flow: 555 GPH
Drain pipe inner diameter: ≥ 1.5 in
Return pipe inner diameter: ≥ 0.79 in
Power-outage buffer volume: 4.1 US gal

Chamber layout (underflow / overflow alternating)

Chamber	Clear width	Clear depth	Volume
Drain / mechanical	7.52 in	13.31 in	6.4 US gal
Biological	7.52 in	13.31 in	6.4 US gal
Return pump	7.52 in	13.31 in	6.4 US gal
Extra chamber	7.52 in	13.31 in	6.4 US gal

超限

The sump exceeds the free space inside the cabinet (available 1050 mm × 350 mm × 643 mm) and was clamped to 800 mm × 350 mm × 380 mm; otherwise it would clash with the legs, rails and top board
The tooth height 24 mm exceeds the space above the rim (water surface 15 mm below the rim) and was clamped to 15 mm
The drain bore 25 mm is smaller than the 38 mm recommended for the turnover rate; the overflow may not keep up

Sump glass cutting plan (summary)

Sump glass totals 51.34 m² (including the main tank).

Bottom panel31.5 × 13.78 × 0.24 in
Front panel31.5 × 14.72 × 0.24 in
Back panel31.5 × 14.72 × 0.24 in
Left side panel13.31 × 14.72 × 0.24 in
Right side panel13.31 × 14.72 × 0.24 in
Baffle 1 (underflow)13.31 × 11.04 × 0.24 in
Baffle 2 (overflow)13.31 × 13.74 × 0.24 in
Baffle 3 (underflow)13.31 × 11.04 × 0.24 in

Notes

Drain sizing assumes gravity flow of about 240 GPH per 1 in inner diameter, plus a 20mm margin; actual flow depends on drop and elbows
The sump operating water level is set by the last overflow baffle; leave buffer volume for the backflow during a power outage
The return pump chamber has the lowest water level and must not run dry in operation (avoid dry running)

The calculator above follows the unit system selected at the top of this page; the explanatory text below stays metric (mm / L / kg / ℃).

Need a full design?

Want to turn the dimensions into a 3D model and a complete bill of materials: Enter length, width and height in the aquarium designer and it generates the 3D model, dimensions, glass cut list, silicone usage and equipment selection, all exportable as CSV and PNG.

How to use it

Step 1Set the turnover flowUsually 5~8× the total system volume per hour; a marine reef tank can go to 10×, but pushing higher makes water pass through the filter chambers too fast.
Step 2Convert to a drain pipe diameterUnder gravity, each 25mm of internal diameter carries about 900 L/h; add a 20mm margin and round up to the next standard pipe size.
Step 3Lay out the chambersAlternate underflow and overflow baffles to create the chamber sequence: mechanical filtration, biological filtration, return pump.
Step 4Check the buffer volumeThe sump has to hold whatever drains back from the main tank overflow box and pipework during a power outage, typically around 20% of the sump volume.

Frequently asked questions

How many chambers should a sump have?: Three is common: a drain / mechanical chamber for filter wool and the protein skimmer, a biological chamber for media, and a return chamber for the pump and heater. More chambers are easier to fine-tune, but each chamber should be a whole 20mm multiple in clear width, or the water level will swing too much.
How large does the drain pipe need to be?: Estimating on gravity flow, each 25mm of internal diameter carries about 900 L/h. For a 350L system at 6× turnover, that is 2100 L/h and needs about 58mm of internal diameter, so take a standard 60mm; with a dual drain you could use 32mm on each.
Will a power outage flood the floor?: Everything above the water level in the main tank overflow box drains back down under gravity. The smaller the overflow box and the lower the pipe intake, the less comes back. Always leave at least 20% of the sump as buffer volume, and make sure the return chamber cannot be pumped dry and burn out.
Why does the return chamber water level drop?: Evaporation and clogged filter wool both lower the water level in the return chamber, while the other chambers stay put because their level is set by the baffles. So the return chamber needs allowance for evaporation, or an auto top-off.
How do I set baffle heights in a sump?: An underflow baffle (water passes underneath) sets the minimum water level in that chamber; an overflow baffle (water spills over the top) sets the maximum water level in the chamber upstream. Stepping them down progressively reduces bubbles, and the last overflow baffle sets the running water level in the return chamber.