How To Build a Sump - DIY Sump Baffle Kit
A sump is an essential filtration system for many reef aquariums, providing increased water volume, better filtration, and a space to hide equipment such as protein skimmers and heaters. By setting up a sump, you improve water stability, reduce clutter in your display tank, and allow for more advanced filtration options like refugiums and reactors.
Using a DIY sump baffle kit, like the Fiji Cube 40-Gallon Breeder Sump Baffle Kit, building a sump yourself is easy and affordable! Simply adhere the precisely cut baffles into a standard-size glass or acrylic aquarium to create designated sections for filtration. In this guide, we’ll walk you through the process of assembling a sump using this kit with a 40-gallon glass aquarium, which is a popular choice due to its size and versatility.
Helpful Tip: Always choose a sump that is large enough to hold at least 25% of the total system water volume.
Materials Needed
- Fiji Cube 40-Gallon Breeder Sump Baffle Kit (Available here)
- 40-Gallon Breeder Tank (standard dimensions: 36" x 18" x 16")
- Silicone Sealant (aquarium-safe)
- Caulking Gun
- Rubbing Alcohol & Paper Towels (for cleaning glass before sealing)
- Masking Tape (to help position baffles while sealing)
- Plastic Razor Blade or Scraper (for smoothing silicone)
- AquaMesh Filter Sheets (optional, for additional sump dividers)
- Acrylic Solvent / Glue for assembling the filter sock holder
- Rubber Gloves
Step 1: Plan Your Sump Layout
Before installing the baffles, familiarize yourself with the sump sections:
- Drain & Skimmer Section – Where water from the display tank enters.
- Bubble Trap – A series of baffles designed to reduce air bubbles.
- Refugium or Media Section – Can be used for biological filtration, macroalgae, or filter media.
- Return Section – Houses the return pump that sends water back to the display tank.
Step 2: Clean the Tank & Baffles
Clean the inside of the tank with rubbing alcohol and paper towels to remove any dust or residue. Wipe down the acrylic baffles with a clean, dry cloth to ensure a good silicone bond.
Step 3: Assemble The Filter Sock Holder & Install the First Baffle
- Assemble the filter sock holder with baffle according to Fiji Cube instructions using acrylic solvent.
- Place the sock holder with baffle into your aquarium, and set up tightly against the wall of the aquarium. Use masking tape to secure it if needed.
- Use painters / masking tape to create a clean caulking line. Run the tape inside the aquarium about 1/4" from the baffle seam. (see video)
- Apply a generous bead of silicone along the edges where the baffle will contact the glass. Be sure to fill all the gaps with silicone.
- Remove masking tape to create a clean silicone line.
- Let it cure for about 30 minutes before proceeding.
Step 4: Install the Bubble Trap Baffles & Return Pump Section
The bubble trap consists of two baffles. One adjustable baffle to set the water level in the skimmer section and the final return baffle the water will flow under.
Return Baffle
- Start with the final return baffle which has a gap for water to flow under it. Position it about 6" from the end of the aquarium leaving enough room to fit your return pump in the final chamber.
- Run masking tape along both sides of the baffle about 1/4" from the seam.
- Apply a generous bead of silicone along the edges where the baffle will contact the glass. Be sure to fill all the gaps with silicone.
- Remove masking tape from ONE SIDE of the baffle to create a clean silicone line.
- Let it cure for about 30 minutes and remove the final strip of masking tape.
Adjustable Baffle
- Remove the adjustable plastic weir from the baffle itself.
- Using the spacers, set the baffle inside the sump about 1.5" from the return baffle (see video).
- Ask for help and have another person hold the baffle while you silicone it into place.
- Once cured, attach the adjustable weir to the baffle.
Helpful Tip: Place spacers or cardboard strips temporarily to maintain even gaps while sealing if needed. Use masking tape to secure baffles while they cure.
Step 5: Install The Divided Baffle
Install the final divider baffle into the protein skimmer chamber if you need it. This will allow you to separate your protein skimmer from a refugium section or dedicated media chamber. Be sure to space the baffle so your protein skimmer will fit into the appropriate chamber.
Step 7: Let the Silicone Cure
Allow the silicone to cure for 24–48 hours before testing with water. Once fully cured, check all seams and clean up any excess silicone with a plastic razor blade.
Helpful Tip: A great way to create additional sections within the sump, such as separating filter media or a refugium, is using AquaMesh filter sheets. Simply cut them to size and wedge them between baffles to form extra compartments without permanent modifications.
Step 8: Leak Test the Sump
- Fill the sump slowly with freshwater to test for leaks before connecting it to your display tank.
- Let it sit for several hours and check for leaks around the baffles.
If everything looks good, drain and dry the sump before installing it under your aquarium.
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