An acrylic sump baffle is a flow-control device built from a flat sheet, and the numbers that matter are water level, weir height and the gap under the last baffle. Get those wrong and the symptom is a pump running dry or a skimmer that never settles.
A reef keeper in Hamburg built a 900 mm sump with three compartments and a bubble trap. The return pump ran dry within a week of every water change, because the last baffle sat 40 mm off the base and the running volume was smaller than the evaporation margin.
Acrylic sump baffle layout: levels and weirs
- Baffle height: running level plus 20 mm freeboard
- Under-gap: 20 to 25 mm on the last baffle
- Bubble trap: three baffles at 25 mm spacing, over-under-over
- Thickness: 6 mm to 450 mm height, 8 mm above
The freeboard is the detail that prevents a floor flood. A baffle exactly at the running level leaves no volume for the water that drains back when the pump stops, and the sump overflows on the next restart.
Bubble traps and the joints that stay put
A bubble trap is three baffles: water passes over the first, under the second and over the third, at 25 mm spacing. Tighter spacing increases velocity and carries bubbles through; wider spacing lets them rise.
Joints decide whether the sump stays watertight for years. Silicone bonds to glass and acrylic and can be removed with a blade, which is why retrofit baffles use it. Solvent welding gives a stronger joint but only between two acrylic surfaces, and it cannot be undone.
Where the baffle meets the sump wall, a 3 mm silicone fillet on both sides prevents a slow leak that shows up as a damp patch rather than a visible gap.
For the viewing panels and tank walls that share the same material, the fabrication notes are in acrylic aquarium viewing panels, and the bonding agents are listed in the acrylic chemical resistance guide.
Send your sump dimensions, pump flow and skimmer model to oversales@rpplexiglass.com for a baffle kit quote.
Frequently Asked Questions
What thickness acrylic for a sump baffle?
6 mm for baffles up to 450 mm high in a sump under 1.2 m, 8 mm for taller or wider compartments. Baffles hold water head, so thickness follows height rather than tank size.
How high should a sump baffle be?
The running water level in that compartment, typically 200 to 250 mm in a sump 400 mm deep. A baffle set at the rim leaves no freeboard for a pump stop and the sump overflows on restart.
Silicone or solvent weld for sump baffles?
Silicone for a retrofit into an existing sump, because it bonds to glass and to acrylic and can be cut out. Solvent weld only where two acrylic faces meet and the joint will never need removing.