How to Set Up an Aquarium Sump Filter: Complete Beginner Guide
A sump filter transforms how you manage a large aquarium — moving mechanical and biological filtration out of the display, adding significant water volume to the system, and giving you a hidden space for equipment. For tanks above 200 litres, a sump is often the best filtration choice available. Knowing how to set up an aquarium sump filter properly from the start prevents the leaks, floods, and equipment failures that turn this upgrade into a nightmare. Gensou Aquascaping at 5 Everton Park, Singapore has built sump systems into countless installations across the island over more than 20 years.
Understanding What a Sump Does
A sump is a secondary tank, typically placed in the cabinet below the main display, connected by a drain (overflow) and a return pump. Water overflows from the display tank into the sump, passes through filter media, and is pumped back up. The sump also houses heaters, protein skimmers (for marine tanks), dosing lines, and any other equipment you want out of the display. In freshwater planted tanks, the sump houses biological media and provides stable conditions for beneficial bacteria away from light and fluctuation.
Sizing Your Sump Correctly
A sump should hold at minimum 20–30% of your display tank’s volume. For a 300-litre display, a sump of 60–100 litres is appropriate. More importantly, size the sump to handle the siphon break volume — the amount of water that drains from the display pipes when the return pump stops. Calculate this by measuring how far below the water surface your overflow intake sits, then ensure the sump has that spare capacity before it would overflow. Test this in a controlled way before commissioning the system fully.
Choosing an Overflow System
Display tanks drain into sumps via one of three methods: a pre-drilled bulkhead, an external overflow box with a siphon, or an in-tank overflow box. Pre-drilled is the most reliable — no siphon to break, no risk of flooding from siphon failure. Overflow boxes work well but require a reliable standpipe configuration (Herbie method or Durso standpipe) to prevent gurgling. Aquariums purchased without pre-drilled holes can be professionally drilled by Gensou Aquascaping or other local glass specialists for around $50–100 per hole.
Plumbing Basics
Use PVC pipes of at least 25 mm diameter for the drain and 19–25 mm for the return line. Larger pipe means quieter operation and lower risk of blockage. PVC fittings and primer/cement are available from hardware stores including Horme and Home-Fix across Singapore at modest cost. Silicone-seal all bulkhead fittings inside and outside; allow 24 hours cure time before testing with water. Union fittings on the return pump allow for easy removal without cutting pipes during maintenance.
Filter Media Layout Inside the Sump
Divide the sump into sections using baffles — silicone-bonded acrylic or glass dividers. The first section receives raw overflow water and holds coarse mechanical filtration: filter sock (a fine mesh bag catching solids) or coarse foam. The second, larger section holds biological media — ceramic rings, sintered glass, or plastic bio-balls — where nitrifying bacteria colonise. The third section, the return chamber, houses the return pump. Keep the return chamber water level stable; fluctuating levels indicate evaporation and require auto top-up.
The Return Pump
Size the return pump to turn over the display tank volume two to four times per hour via the sump, accounting for head pressure losses from the vertical lift and pipe bends. For a 300-litre display at 1.2 metres of head, a pump rated at 1,500–2,000 litres per hour at zero head is appropriate. Variable-speed pumps from brands like Jebao or Eheim Compact+ allow fine-tuning and reduce noise. Always place the pump fully submerged — never run a submersible pump dry, even briefly.
Commissioning and Leak-Testing
Fill the sump manually with conditioned water before starting the return pump for the first time. Run the return pump at low speed while someone watches every connection for drips. Allow the system to run for 24 hours with you checking periodically before leaving it unattended. In Singapore, a sump cabinet made of wood or MDF requires marine-grade sealing or a waterproof liner inside — any slow leak over months will cause timber damage and potential floor issues, particularly in HDB flats where floor loading and water damage to neighbours below is a concern.
Ongoing Maintenance
Rinse the filter sock weekly in old tank water (never tap water) or replace it. Clean biological media only when flow through it visibly decreases — healthy biomedia should never be rinsed aggressively. Top up evaporation losses with fresh RO or conditioned water, not saltwater. A well-maintained aquarium sump filter setup runs reliably for years and makes large tank management dramatically simpler than relying solely on hang-on-back or canister filtration.
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