How to Build a DIY Aquarium Sump From Scratch
A sump is the single most versatile upgrade you can make to any aquarium system — it increases water volume, hides equipment, and provides space for biological filtration that no canister filter can match. This build DIY aquarium sump guide from Gensou Aquascaping at 5 Everton Park, Singapore, walks you through designing and constructing a functional sump from a standard glass tank, with materials readily available from local aquarium shops and hardware stores.
Choosing a Sump Tank
Your sump should be 30-50% of your display tank’s volume for optimal benefit. For a 300-litre display, a 90-120 litre sump works well. A standard 90 cm x 30 cm x 35 cm glass tank is a common and affordable starting point — expect to pay $30-$60 at shops around Serangoon North or C328 Clementi.
The sump must fit inside your aquarium stand with clearance for maintenance access. Measure the internal dimensions of your cabinet carefully, accounting for the return pump, pipes, and your hands reaching in for cleaning. Leave at least 10 cm of space above the sump for overflow capacity when the return pump is switched off.
Planning the Baffle Layout
Baffles are glass or acrylic dividers that create separate chambers within the sump. A typical three-chamber design works as follows: the first chamber receives water from the overflow and houses mechanical filtration, the second chamber holds biological media, and the third chamber contains the return pump. Baffles force water to flow over and under alternating walls, slowing flow and maximising contact time with filter media.
Cut baffles from 5 mm glass — a local glass shop can cut pieces to your exact dimensions for under $10. Three baffles are standard: two rising from the bottom with a gap at the top, and one suspended from the top with a gap at the bottom. This over-under-over pattern traps bubbles and debris effectively.
Siliconing the Baffles
Use aquarium-safe silicone only — standard bathroom silicone contains fungicides toxic to fish. Apply a generous bead along both sides of each baffle, pressing firmly into position. Brace the baffles with tape or clamps and allow 48 hours for full cure. In Singapore’s humidity, silicone cures well but needs adequate ventilation to off-gas acetic acid during the process.
Test the sump by filling it with water and checking for leaks around every baffle joint. Fix any seepage by applying a second silicone bead over the suspect area and curing for another 24 hours. Patience here prevents flooding your cabinet later.
Mechanical Filtration Chamber
The first chamber catches debris before it reaches biological media. A filter sock over the drain inlet is the most efficient option — 200-micron polyester socks cost $3-$5 each and trap fine particles that would otherwise cloud your water. Replace or wash them every three to five days to prevent nitrate buildup from trapped organic matter decomposing.
Alternatively, stack coarse, medium, and fine foam pads on a simple egg-crate shelf. This is lower maintenance than filter socks but less effective at polishing water clarity. Rinse foam pads in old tank water during water changes — never under tap water, which kills beneficial bacteria.
Biological Filtration Chamber
This is the engine of your sump. Fill the middle chamber with high-surface-area biological media: ceramic rings, sintered glass (such as Seachem Matrix), or plastic bio-balls. A 10-litre volume of quality bio media supports a heavily stocked 300-litre display tank. Avoid packing media too tightly — water must flow through freely, not channel around blocked sections.
For planted tanks or reef systems, consider incorporating a refugium section with macroalgae (marine) or fast-growing stem plants (freshwater). This provides natural nutrient export, competing with nuisance algae in your display. A small LED grow light over the refugium on a reverse daylight schedule stabilises pH overnight.
Return Pump Selection and Plumbing
Choose a return pump that delivers 5-10 times your display tank volume per hour after accounting for head loss. For a 300-litre tank with the sump 1 metre below, a pump rated at 3,000-4,000 litres per hour at zero head will deliver approximately 2,000-2,500 litres per hour at 1 metre head — right in the target range.
DC pumps from brands like Jebao or Reef Octopus offer adjustable flow and quieter operation than AC pumps, with prices starting around $60-$120 on Shopee. Connect the return line with 20 mm PVC pipe, using a ball valve above the pump to fine-tune flow rate. Include a check valve or drill a small anti-siphon hole in the return pipe 3 cm below the display tank waterline to prevent back-siphon during power outages.
Overflow Design and Drain
Water reaches the sump via an overflow. Drilled tanks with a bulkhead fitting are the most reliable option — have your glass shop drill a hole before setup, as drilling a filled tank is impractical. A Durso standpipe inside the overflow box silences the drain, eliminating the gurgling noise that plagues basic overflow designs.
If drilling is not an option, hang-on-back overflow boxes with siphon tubes work but are less reliable. The siphon can break during power outages, requiring a restart. For a build DIY aquarium sump guide that prioritises reliability, a drilled overflow is always the recommendation from experienced hobbyists and professionals at Gensou Aquascaping alike.
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5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
