This sump & refugium is designed to fit under a smaller tank. Dimensions are 26" x 18" x 16" and can also be made cube shaped (20" x 20" x 16" for example). What is nice about this sump is that the refugium spans the entire front so you can enjoy seeing the macro algae grow and the pods scurrying about.
The refugium area is the full width across the front, and that section is 26" long, 6" wide and 12" tall, holding about 8.5 gallons of water. Note: The baffle is 13" tall, but the water level will be 12" tall where it pours through the teeth.
25% of the water draining from the tank will enter directly into the refugium, in this case on the right side via an elbow fitting. It will pour through the teeth into the rear section called the "return section" where the return pump will be located. Water enters this sump in two zones at once, and then flows into the return zone.
This top view shows the refugium in the front (bottom portion), with the return section to the left side, and the skimmer section to the right side. A bubble trap divides the two rear sections to stop microbubbles from being sucked into the return pump.
The majority of the water draining from the tank will enter the corner bubble tower. This can be filled with small pieces of live rock rubble to break up the bubbles. Water flows through the teeth and into the skimmer section. This section is 13" x 11" x 9" to hold an ASM skimmer. Water will flow from this section through the bubble trap and into the return section.
The sump has been turned around so you can view the rear section. The bubble trap is designed in an over-under-over layout, with a 1" gap between each baffle. As long as the flow going through this sump is 3x to 5x the volume of the display tank, microbubbles should not be an issue.
Still looking at the sump from the back side, the teeth are visible. Water from the refugium will flow through these teeth and into the return section. Water pours quietly and gently, and bubbles are not generated.
The top flange of this sump is 1.25" wide.
This sump can hold 30g to the top. When running normally, it will hold about 18g of water, leaving room for 12 more gallons in the event the pump is off for any reason. Anti-siphon holes are a must!
An automatic top-off system is pretty much a must for this sump, because the return section is quite small. Only a little evaporation can result in that section's water level lowering too much causing the return pump to suck in air, which would cause a rush of bubbles to pump into the main tank.
A longer light strip is needed to light the narrow refugium zone, such as a LED fixture. Consider what light you'll use, because you'll need to either move the light out of the way or reach over it to remove the skimmer's collection cup or handle reactors and other gear.