DIY Glass Aquarium Sump - Coral Ever After

As someone who has made a few glass aquarium sumps and one fully customized acrylic sump (along with owning pre-manufactured ones), I don’t understand the excitement over acrylic sumps. Glass aquarium sumps are cheaper, easier to build, and hold up to abuse better than acrylic for the average user. I buy non-reef-ready aquariums at the local pet store “$1/gallon sale,” design the sump, and then get some glass cut. This is how I made a 40g glass sump for $65. (Or, if the idea of getting glass cut is too daunting or time-consuming, consider these pre-cut baffle kits!)

Supplies List:

This is a list of what I actually used to build my glass aquarium sump, along with estimated prices as of the published date. I’ve included links to the products (or similar) (please note, as an Amazon Associate, I earn from qualifying purchases. I get commissions for purchases made through links in this post.)

Glass Aquarium Sump Instructions:

Step 1: Design the Glass Sump Layout

Designing the setup may be the most challenging aspect of this project, and I highly recommend that you research various designs prior to starting. Consider skimmer footprints, algae reactors, probes, return pump size, and sizes/ locations of all the other equipment you’ll need or may want in the future. As you’ll see below, sump design really deserves its own post (or multiple!)

The Footprint:

Design needs/desires lead to determining your equipment requirements. If, for example, the skimmer has a footprint of 10 inches by 10 inches and requires a water depth of 8 inches, then the sump will be quite sizeable. Start drawing out the footprint design on the graph paper, following a similar train of thought for the water height. I like to stay simple with sump designs. The water drains into a filter sock, into a skimmer, through some baffles (to help minimize the bubbles from the skimmer), slowly over a refugium, slowly over a deep sand bed, through more baffles, to the return pump, and out.

The Height:

Next, you’ll need to account for the water that overflows from the main display aquarium and drains into the sump. Leave enough space for that water plus a few extra gallons just to be on the safe side. For instance, if your display tank water level drops by two inches when the pumps are off, then you can multiply that by the tank’s length and depth to have an estimate of the water volume (in cubic inches) draining to the sump. Convert the cubic inches to gallons (there are plenty of easy calculators online), and that will be the water volume going to the sump. This is a safety margin, which must be added to the planned water level height. Personally, I like to oversize my sump (another 50-100% more) just in case anything happens (e.g., tank continues to drain). This will also help to account for water volume that was above the water line in an operational skimmer, in the case of a power outage.

The Volume:

With the water footprint and height set, once again, calculate the volume required (length x width x height, converted volume to gallons). This is the tank size you will need to purchase, if not larger for a greater safety margin. I used a 40 gallon breeder aquarium for this project.

40 Gallon Glass Aquarium Selected for my Sump

Once the basic footprint is complete, it is time to design the baffles. The depth is just the inside depth of the empty aquarium, and the height is the running water level height (not the overflowed water). Placing some at staggered heights can cause the water to move above and below them, thus removing some bubbles. Play around with the design, and try to visualize water moving through your sump design.

Step 2: Cutting the Glass Baffles

Once the design is complete, measure the pieces of glass you’ll need. If your local glass shop will let you (and if the tank is small), take the tank with you so the glass company can custom-fit the glass to the tank. Tank sides are rarely truly parallel, so the baffles may need trimming. I also recommend having the glass shop sand the edges of the glass to prevent injury during installation. My local glass shop only charged me $20 for the glass, cutting/polishing, and sizing. They were amazing!

Step 3: Installing the Baffles

Use a high-quality silicone made for aquarium use. I chose black for the sump, but it is also readily available in clear. Do NOT use bathtub silicone as it frequently contains an anti-mildew chemical in it that can foul an aquarium. Home improvement stores often carry the proper silicone, and local fish stores often do as well. Use only in a well-ventilated area as the fumes are not pleasant and may cause health problems. It didn’t take much; I only used half of the tube shown.

Use a measuring tape and right angles to place the first baffle. Work the smallest areas to the largest areas to prevent areas that are difficult to seal. I worked on the left, right, then center.

I use duct tape to hold the baffles in place while it dries. Let each area sit for an hour or two before moving to the next section. This helps prevent silicone slips.

Step 4: Adding a Filter Sock Holder

If you decide to add a filter sock holder, there are lots of designs available. Just make sure yours has a bracket that will fit onto the side of the aquarium sump. I’ve added bonded acrylic ones before (shown in the photo below), but it is challenging to make a good bond between glass and acrylic. After a couple years (if you’re lucky), they will likely require resealing. Using glass filter sock holders is just too dangerous, in my opinion.

Step 5: Curing

Once the build is complete, let it cure according to the silicone manufacturer’s instructions (this is typically 24 hours, although 48 hours is likely better). If possible, continue to let it sit in a well-ventilated area. After the silicone has cured, remove the duct tape and layout angles. Remove any silicone drips or other debris.

Step 6: Test it Out!

With the build complete, it is time to test the sump! Fill the sump to the running water level (lowest baffle height). All baffles should hold, with no flexing or leaking (if it does, just drain, dry, reseal, and retest). If all looks good, then you’re all finished! It’s time to install it on the tank! Mine is shown below, with the tank draining into the left, flowing through a skimmer and live rock, under and over baffles, over a lighted refugium area with baffle, over a flex-use area with baffle, then down, under, and over baffles into the return section.