If you've made it this far, you probably already know that a sump is essentially a second aquarium that is connected to the main display tank with plumbing and a return pump.
It's a place to house your filtration and life support equipment like:
- Protein Skimmer
- Media Reactor
- Biological Media
- UV Sterilizer
- Algae Scrubber
- Filter Socks
- Auto Top Off System
- Heaters
- Controller Probes
- Dosing Lines
- And More
A sump is a great way to keep everything out of sight, leading to a cleaner and more professional-looking display tank. It also allows for easier access to the equipment for maintenance and adds additional water volume to the system, helping improve overall water chemistry stability.
A sump itself is not filtration, but it's the foundation of a good saltwater aquarium filtration system because it helps direct water where it needs to go.
Water flows from the display tank into the sump, passes through the filtration chambers, and is pumped back into the aquarium.
Why Build a DIY Sump?
The choice to build a DIY sump vs. buying something pre-made usually comes down to a combination of cost and customization.
Cost
Doing the work yourself can save you a few hundred dollars vs. buying a pre-made sump. For reefers that don't need anything flashy to house the filtration gear hidden away in their aquarium stand, a DIY sump is a no-brainer way to cut cost without affecting performance. Less money spent on a sump just means more money for fish and coral, right?
Customization
Building a DIY sump means you control where the baffles go, how large each chamber is, and what type of filtration the sump is designed to support. You can size the equipment chamber around your protein skimmer, create a dedicated refugium, leave extra room for media reactors, or build a larger return section to reduce how quickly the water level drops from evaporation.
How to Build a DIY Sump
DIY sumps most commonly start with a standard black-trim glass aquarium from a big box pet store. These aquariums are popular because they come in several different sizes and are inexpensive. From there, reefers can pick up some glass or acrylic, cut it to size, and silicone it in place to create a baffle system.
For this demonstration, we'll be using the Fiji Cube Sump Baffle Kit. If you're also drilling your own display aquarium like we did, the Fiji Cube LoPro External Overflow Boxes are our go-to choice.
Tools and Supplies You’ll Need
- Glass aquarium
- Pre-cut sump baffle kit or individual glass or acrylic baffles
- Aquarium-safe silicone (and drip-free caulk gun, if necessary)
- Tape measure
- Speed square
- Permanent or dry-erase marker
- Paper towels
- Disposable gloves
- Painter's tape
- Silicone finishing tool or old plastic credit card
Step 1: Clean and Dry the Aquarium
Remove any labels, stickers, or adhesive from the aquarium. Thoroughly clean and dry the inside glass, paying special attention to the areas where the silicone will make contact. The glass must be clean and completely dry for the silicone to form a strong bond.
Step 2: Identify the Baffles and Plan the Layout
Lay out all of the baffle pieces and identify where each one belongs. In a typical sump layout, water enters through the filter sock or mechanical filtration section, moves through the main equipment chamber, passes through a bubble trap, and finishes in the return pump chamber.
If you're cutting your own baffles, use this time to determine the number, position, and spacing of each piece before installation.
Step 3: Dry Fit the Baffles and Equipment
Place the baffles inside the aquarium without silicone and assemble the complete sump layout. Then, place the equipment you plan to use inside its intended chambers.
Confirm that the protein skimmer, return pump, heaters, and any other equipment fit comfortably. Make sure there is enough room to remove each piece of equipment for cleaning and maintenance.
Step 4: Square and Mark the Baffle Positions
Once you're happy with the layout, use a tape measure and speed square to make sure each baffle is positioned correctly and sitting straight. Mark the final location of each baffle on the outside of the aquarium with a marker.
Take your time during this step. Once the silicone cures, moving the baffles or changing the chamber sizes becomes much more difficult.
Step 5: Apply Painter's Tape
Apply painter's tape along both sides of each planned silicone seam. Place tape on the baffle and on the aquarium glass, leaving a small gap where the silicone bead will be applied.
This step is optional, but it makes it much easier to create straight, clean-looking seams and reduces the amount of silicone that needs to be cleaned up afterward.
Step 6: Silicone the First Baffle in Place
Position the first baffle using the marks you made during the dry fit. Apply a continuous bead of aquarium-safe silicone along each edge where the baffle meets the aquarium glass.
Smooth the silicone along the seams using a silicone finishing tool, a gloved finger, or an old plastic card. Make sure the silicone fills the joint without leaving large gaps or air pockets.
Step 7: Install the Remaining Baffles
Repeat the silicone process for each remaining baffle. Check the position of each piece as you work to make sure it stays straight, square, and properly spaced.
Be careful not to bump previously installed baffles while working on the next section.
Step 8: Remove the Painter's Tape
Remove the painter's tape before the silicone begins to skin over. Pull the tape away slowly to leave behind clean edges along each seam.
Use a paper towel to carefully clean up any excess silicone without disturbing the finished seams. Alternatively, you can wait until the silicone fully cures and clean any messes up with a sharp razor blade.
Step 9: Allow the Silicone to Fully Cure
Leave the sump in a clean, dry, and well-ventilated area while the silicone cures. Follow the full curing time listed by the silicone manufacturer and do not add water until it is completely cured.
Many aquarium-safe silicones require 24 hours to cure, but some products may require more time.
Once the silicone has fully cured, inspect each seam and confirm that the baffles are secure. You can test each individual chamber for leaks if you wish, but since we're building this all inside an already assembled aquarium, a tiny leak shouldn't make any functional difference in most cases.
Congrats! Your DIY sump is now ready for equipment, plumbing, and final installation beneath the display tank.
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