Sump & Refugium Guide: Design, Plumbing & Setup
Everything you need to know about adding a sump and refugium to your reef aquarium — from choosing the right overflow and plumbing to growing macroalgae and cultivating copepods. Compiled from the best practices of Melev’s Reef, Bulk Reef Supply, Gmac Reef, AlgaeBarn, ReefBum, and the reef keeping community.
1. What Is a Sump?
A sump is a separate container — typically positioned in the cabinet beneath your display tank — that receives water via an overflow, processes it through various filtration stages, and returns it to the display via a return pump. As Melev’s Reef explains, a sump provides “greater control over your reef or fish-only display tank” by increasing total system volume, hiding equipment, and stabilizing water chemistry [1].
Why Every Reef Tank Needs a Sump
Extra Water Volume
- A 30-gallon sump on a 75-gallon display adds 40% more water volume, diluting pollutants and buffering parameter swings [1]
- More water = more thermal mass, meaning slower temperature changes and more stable chemistry
- Evaporation occurs in the sump (not the display), so display water level stays constant [1]
Filtration Stages
A well-designed sump provides three types of filtration in sequence: mechanical (filter socks and foam blocks remove particles), chemical (activated carbon and GFO remove dissolved organics and phosphate), and biological (live rock rubble, macroalgae, and beneficial bacteria convert ammonia to nitrate) [2]. The protein skimmer adds a fourth layer, physically removing dissolved organic compounds before they break down [1].
2. Three-Chamber Layout
The most common and proven sump design divides the container into three main chambers separated by glass or acrylic baffles. Water flows from one end to the other by gravity, passing through each filtration stage in sequence [3].
Intake / Filter Sock Chamber
Water from the display enters through the drain line and drops into a filter sock (typically 100–200 micron felt or mesh) that catches detritus, uneaten food, and particulate waste before it dissolves [2]. This chamber may also house a filter roller (automated fleece filter) for hands-free mechanical filtration. Change filter socks every 2–3 days to prevent nitrate accumulation [5].
Skimmer Chamber / Refugium
The middle chamber is the largest section and typically houses the protein skimmer. Skimmers work best with a stable water level, so this chamber should maintain constant depth (usually 7–10 inches depending on the skimmer model) [1]. In many modern sumps, this area is divided further with one side for the skimmer and the other for a refugium growing macroalgae and pods [3]. Carbon and GFO media reactors or media bags also live in this section.
Return Pump Chamber
The final chamber houses the return pump that pushes processed water back up to the display. This is the only section where water level fluctuates due to evaporation [1]. ATO (auto top-off) sensors sit here to replenish evaporated freshwater. Keep the water level high enough that the return pump never runs dry, but leave headroom to absorb back-siphoned water during a power outage [4].
Bubble Trap Baffles
Between the skimmer chamber and return chamber, install a bubble trap — three baffles positioned in sequence (down-up-down or up-down-up) with the center baffle raised 1 inch from the sump floor [1]. Space the baffles approximately 1 inch apart. Water is forced to change direction multiple times, releasing trapped air bubbles before they reach the return pump and get blasted into the display as unsightly microbubbles [1].
3. Plumbing Basics
Getting water from the display to the sump and back requires reliable plumbing. The two critical components are the overflow (display to sump) and the return line (sump to display).
Overflow Types
The overflow is how water leaves the display tank. There are three widely used drain methods, each with different noise levels and fail-safe characteristics [6]:
| Overflow Type | Drain Lines | Noise Level | Fail-Safe | Best For |
|---|---|---|---|---|
| Durso Standpipe | 1 | Moderate | Low | Budget builds, simple setups |
| Herbie Method | 2 (siphon + emergency) | Silent | Medium | Most reef tanks |
| Bean Animal | 3 (siphon + open channel + emergency) | Silent | High | SPS tanks, large systems |
Durso Standpipe
The simplest overflow design: a single PVC standpipe with an air hole at the top that breaks the siphon effect and reduces the gurgling noise of open drains. While quieter than an open pipe, it can still produce a flushing sound as water levels fluctuate. Best suited for smaller tanks or budget builds where simplicity is paramount [6].
Herbie Method [6]
Uses two drain lines: a primary siphon drain (fully submerged, tuned with a gate valve to match return pump flow exactly) and an emergency drain (open standpipe set slightly higher). When properly tuned, the Herbie method “can completely silence your aquarium drain and eliminate microbubbles” [6]. If the siphon drain clogs, the emergency drain takes over with an audible gurgle that alerts you to the problem.
Bean Animal
The gold standard for reliability. Uses three drain lines: a full siphon (silent primary drain), an open channel (trickle backup), and a true emergency (dry standpipe). Even if the primary siphon fails, the open channel handles the flow quietly. The emergency line only activates if both primary and secondary fail. Requires three bulkheads, making it less practical for small overflows but ideal for serious reef builds [6].
PVC Plumbing Essentials
- PVC Schedule 40 is the standard for aquarium plumbing — pressure-rated, widely available, and easy to cut/glue [7]
- Common drain sizes: 1″ (300 GPH capacity) or 1.5″ (750 GPH) per drain line [1]
- Return lines: typically ¾″ or 1″ PVC, stepped up from the pump output to reduce head loss
- Every 90° elbow adds approximately 1 foot of equivalent head loss — minimize them [7]
- Use unions on both sides of every pump and valve for easy maintenance and removal
- Flexible vinyl tubing can replace rigid PVC for tight spaces but adds more friction loss per foot
Flow Rate Guidelines
The return pump should provide 3–5× display tank volume in turnover per hour through the sump [1] [8]. For a 100-gallon tank, that means 300–500 GPH of actual flow reaching the display (after accounting for head loss). Total circulation including powerheads should be 10–15× for mixed reefs and 20×+ for SPS-dominant tanks [1].
4. Refugium Setup
A refugium (“refuge”) is a lighted compartment within or beside your sump that houses macroalgae, live rock rubble, and a sand bed. Its purpose is twofold: natural nutrient export (macroalgae consumes nitrate and phosphate as it grows) and biodiversity (copepods and amphipods breed in the protected environment and get swept into the display as live food) [1] [9].
Sand Bed & Live Rock Rubble
Add a 4–6″ deep sand bed (DSB) of fine aragonite sand to the refugium floor [9]. The upper aerobic layer hosts nitrifying bacteria, while the deeper anaerobic zones enable denitrification — the conversion of nitrate into harmless nitrogen gas. Top the sand with a handful of live rock rubble to provide surface area for beneficial bacteria and hiding spots for pods. The rubble acts as an anchor for macroalgae and prevents it from tumbling into the return pump [9].
Macroalgae: Chaetomorpha vs. Caulerpa
Chaetomorpha (“Chaeto”)
+ Will not “go sexual” and crash your tank
+ Easy to harvest — just pull out handfuls
+ Excellent copepod habitat (tangled structure)
+ Non-invasive — stays in the refugium
+ Widely recommended by BRS, AlgaeBarn, and ReefBum [9] [10]
- Slower initial growth than Caulerpa
- Needs moderate-to-strong refugium light
Caulerpa
+ Extremely fast growth = rapid nutrient export
+ Thrives in lower light conditions
+ Several species available (racemosa, prolifera, taxifolia)
- Can “go sexual” (sporulate) — releases all stored nutrients back into the water in a milky cloud [10]
- Invasive: runners spread to display tank
- Banned in some states/countries due to invasive potential
- Must keep on 24/7 light cycle to prevent sporulation [10]
Refugium Lighting — The Reverse Cycle
Run your refugium light on a reverse daylight cycle — on at night, off during the day — opposite to your display tank’s photoperiod [9] [11]. This serves two critical purposes:
- pH stabilization: When display lights are off, corals and fish produce CO2 and pH drops. The refugium’s macroalgae is actively photosynthesizing during this time, consuming CO2 and preventing the overnight pH crash [11].
- Constant oxygen: One part of the system is always photosynthesizing, maintaining dissolved oxygen levels 24/7.
Use a grow light in the 5,000–7,000K range or a dedicated refugium LED (Kessil H80, AI Fuge, or Tunze 6255 are popular choices). Aim for 8–12 hours of light per cycle [11]. If your chaeto starts turning white or going pale, increase light intensity or duration.
5. Choosing a Sump
DIY vs. Commercial
DIY Sump
+ Custom fit for your cabinet and equipment
+ Significantly cheaper ($30–80 for a glass tank + baffles) [3]
+ Popular base: 20-gallon long or 40-gallon breeder [3]
+ Add custom chamber sizes for your specific skimmer
- Glass cutting and silicone work required
- Cure time: 48–72 hours for silicone baffles
- Leak potential if baffles are poorly sealed
Commercial Sump
+ Ready to go out of the box
+ Professional baffles and integrated features
+ Often include filter sock holders and probe mounts
+ Warranty and customer support
- More expensive ($150–600+)
- Fixed chamber dimensions may not fit your gear
- Must fit through your cabinet opening
Sizing: 20–30% of Display Volume
The ideal sump should hold 20–30% of your display tank’s volume [2]. For a 75-gallon display, aim for a 15–25 gallon sump. Larger is always better — more water volume equals more stability. Size the sump to fit your stand’s interior dimensions, leaving room for the return pump, skimmer body, and your hands for maintenance.
Popular Sump Models
| Sump | Volume | Tank Size | Refugium? | Type |
|---|---|---|---|---|
| Trigger Systems Ruby 26 | 26 gal | 75–120 gal | Yes | Premium |
| IceCap 30 | 30 gal | 75–150 gal | Yes | Mid-range |
| Fiji Cube 20 Elite | 20 gal | 50–100 gal | Yes | Mid-range |
| Eshopps RS-100 | 22 gal | 75–125 gal | Yes | Mid-range |
| DIY 40-Breeder | 40 gal | 100–200 gal | Custom | Budget |
| DIY 20-Long | 20 gal | 40–75 gal | Custom | Budget |
6. Return Pumps
The return pump is the heart of your sump system. It pushes processed water back up to the display and sets the turnover rate for your entire filtration cycle.
DC vs. AC Return Pumps
DC (Variable Speed)
+ Adjustable flow via controller — dial in exact turnover
+ Quieter at lower speeds
+ Lower energy consumption (30–50% less than AC)
+ Feed mode, ramp-up, and soft-start features
- Higher initial cost
- Controller is a potential failure point
- Some models have shorter lifespans than AC
AC (Fixed Speed)
+ Proven reliability — simple motor design
+ Lower purchase price
+ Long lifespan (5–10+ years)
- Fixed flow — adjust only with a ball valve
- Higher energy consumption
- Louder at full speed
Sizing Formula
Target 3–5× display volume in actual flow delivered to the tank [1] [8]. But pumps lose significant output to head pressure, so you must account for head loss:
1. Measure the vertical distance from sump water level to display return outlet (e.g., 4 feet).
2. Add 1 foot for every 90° elbow in the return line.
3. Add 0.5 feet for every 10 feet of horizontal pipe.
4. Total = effective head height. Look up your pump’s flow curve at that head height.
Example: 100-gal display, 4 ft vertical + two 90° elbows (2 ft) = 6 ft total head. You need 300–500 GPH at 6 ft head. A pump rated at 800 GPH at 0 ft head typically delivers ~400 GPH at 6 ft. [7] [8]
Popular Return Pump Models
| Pump | Type | Max Flow | Max Head | Best For |
|---|---|---|---|---|
| Sicce Syncra SDC 7.0 | DC | 1,900 GPH | 11.5 ft | Large |
| Neptune COR-20 | DC | 2,000 GPH | 16 ft | Apex Users |
| Varios 4 | DC | 1,056 GPH | 9.2 ft | Medium |
| Eheim CompactON 5000 | AC | 1,320 GPH | 12.5 ft | Reliability |
| Sicce Syncra Silent 3.0 | AC | 714 GPH | 10.5 ft | Budget |
7. Copepod & Amphipod Cultivation
One of the greatest hidden benefits of a refugium is its ability to function as a natural live food factory. Copepods and amphipods breed in the protected refugium environment — safe from predatory fish — and are continuously swept into the display by the return pump, providing nutritious live food for wrasses, mandarins, seahorses, and coral-feeding species [9] [12].
Key Pod Species
| Species | Size | Habitat | Best For |
|---|---|---|---|
| Tisbe biminiensis | 0.5–1.0 mm | Benthic (bottom-dwelling) | Mandarin dragonets, wrasses, coral feeding |
| Tigriopus californicus | 1.0–1.5 mm | Pelagic (water column) | Seahorses, pipefish, fry feeding |
| Apocyclops panamensis | 0.5–0.7 mm | Pelagic / benthic | Coral feeding (SPS polyp extension) |
| Gammarus amphipods | 3–10 mm | Rubble / rock | Wrasses, detritus cleanup |
Seeding Your Refugium
Purchase a Starter Culture
Buy a multi-species pod bottle (AlgaeBarn OceanMagik or similar) containing 1,000–2,000+ pods. Add at night with the return pump off for 1 hour so pods settle into the refugium before getting swept away [12].
Provide Habitat
Chaetomorpha is the ideal pod habitat — its tangled, spaghetti-like structure provides thousands of hiding spots and surfaces for biofilm growth (pod food) [9]. Live rock rubble and sand bed complement the chaeto.
Feed the Pods
Add phytoplankton (live or concentrated) 2–3 times per week to feed the pod population [12]. Nannochloropsis and Tetraselmis are the most commonly recommended species. Pods also graze on biofilm and detritus naturally.
Wait & Maintain
Allow 4–6 weeks for the population to establish before adding pod-hungry fish like mandarins. Re-seed every 3–6 months if you have heavy pod predators, or let the population self-sustain if predation pressure is light [12].
8. Common Sump Problems
Microbubbles in the Display
Cause: Air entrainment from the drain line, insufficient bubble trap baffles, or a return pump that is pulling in air. Protein skimmers are also a major source — the effluent water is laden with tiny bubbles [1].
Fix: Ensure your bubble trap has three properly spaced baffles with the center one raised off the floor [1]. Submerge drain line exits below the sump’s water level. Add a filter sponge between the skimmer output and return section. Check for air leaks in plumbing unions above the waterline. If using a Herbie overflow, tune the gate valve until the drain runs completely full with no gurgling.
Overflow Noise (Gurgling / Flushing)
Cause: Air mixing with water in the drain pipe creates turbulence and the characteristic “toilet flush” sound. This is the most common complaint with Durso standpipes and improperly tuned Herbie drains [6].
Fix: For Durso standpipes: adjust the air hole size at the top of the standpipe until you find the sweet spot between silent and siphon-lock. For Herbie drains: slowly close the gate valve on the primary siphon until a tiny trickle of water runs down the emergency standpipe — this means the siphon is handling 99% of the flow silently [6]. Consider upgrading to a Bean Animal for ultimate silence and reliability.
Flooding from Power Outage
Cause: When the return pump stops, water back-siphons through the return line until either the siphon breaks or the sump overflows. Additionally, the overflow box continues draining display water until the water level drops below the overflow teeth [1] [4].
Fix: Drill siphon break holes (½″ below waterline) in the return pipe — this breaks the back-siphon within seconds [1]. Mark a “max fill line” on your sump return section — this is the highest level that can safely absorb back-drain water. Melev notes that typically “2–3 gallons accumulate after power loss” [1]. Test by unplugging the return pump and watching where the water settles — do this before your first real power outage.
Salt Creep
Cause: Saltwater splashes onto surfaces above the waterline, evaporates, and leaves crusty white salt deposits on plumbing, clips, and the sump rim. It is cosmetic but can corrode metal fittings and block air holes over time [5].
Fix: Wipe salt creep weekly with a damp cloth. Use plastic clips and fittings instead of metal wherever possible. Minimize splash by submerging drain outputs and return nozzles. Cover the sump with a loose-fitting lid (acrylic or egg crate) to contain spray while still allowing gas exchange. Check siphon break holes monthly — salt creep can clog them, defeating their flood-prevention purpose [1].
9. Frequently Asked Questions
Do I need a sump for a reef tank?
While not strictly required, a sump is strongly recommended for any reef tank over 30 gallons. It increases total water volume (diluting pollutants), hides equipment from the display, provides stable water levels, and enables refugium-based natural filtration [1]. Smaller nano reefs can succeed with hang-on-back equipment, but a sump dramatically improves stability and maintenance flexibility.
What size sump do I need?
Aim for 20–30% of your display tank volume as a minimum [2]. For a 75-gallon display, a 15–25 gallon sump works well. Bigger is always better — more water volume means more stable parameters. The main constraint is usually your cabinet dimensions. A 40-gallon breeder is the most popular DIY sump base for tanks 100 gallons and up [3].
How often should I change filter socks?
Change or clean filter socks every 2–3 days [5]. Dirty filter socks become nitrate factories as trapped organic waste decomposes. Many reefers keep 5–7 socks in rotation: swap the dirty one, toss it in a bleach-water soak, rinse with dechlorinated water, and air dry. Alternatively, consider an automatic filter roller (fleece filter) for hands-free mechanical filtration.
Is chaetomorpha or caulerpa better for a refugium?
Chaetomorpha is the safer choice and is recommended by the majority of experienced reef keepers [9] [10]. Unlike caulerpa, chaeto will not “go sexual” (sporulate) and dump stored nutrients back into your tank. It is also non-invasive and provides excellent copepod habitat. Caulerpa grows faster but carries the risk of sporulation and can spread runners into the display.
What is the best overflow method for a quiet reef tank?
The Herbie method (two drain lines) offers near-silent operation when properly tuned, and the Bean Animal (three drain lines) is the gold standard for both silence and fail-safe redundancy [6]. Gmac Reef notes the Herbie method “can completely silence your aquarium drain and eliminate microbubbles” [6]. The Durso standpipe is simpler but typically produces some residual noise.
How long does it take for copepods to establish in a refugium?
Allow 4–6 weeks after seeding for copepod populations to establish and begin reproducing in meaningful numbers [12]. Provide chaetomorpha for habitat, live rock rubble for hiding spots, and feed phytoplankton 2–3 times per week. Do not add pod-hungry predators (like mandarin dragonets) until the population is well-established. Re-seed every 3–6 months if predation is heavy.
References
Every factual claim in this guide is cited to its original source. Click any [n] in the text above to jump here.
- Melev’s Reef — “What is a Sump?” (comprehensive sump guide)
- Bulk Reef Supply — “How to Set Up a Reef Tank Sump” (52 Weeks of Reefing)
- Gmac Reef — “40 Gallon Breeder Reef Sump Plans” & DIY Glass Baffles Guide
- Gmac Reef — “Flooding Prevention” — common issues and safety measures
- ReefBum — “Filter Socks for Reef Tanks: Complete Guide”
- Gmac Reef — “Common Aquarium Overflows: Durso, Herbie, and Bean Setups”
- Bulk Reef Supply — “How to Plumb Your Reef Tank” (52 Weeks of Reefing)
- Gmac Reef — “Flow Rate / Turnover” — the 10X rule and system planning
- AlgaeBarn — “The Refugium Guide: Setup, Macroalgae & Benefits”
- ReefBum — “Chaetomorpha vs. Caulerpa: Which Is Better for Your Refugium?”
- Bulk Reef Supply — “The Best Refugium Light for Growing Chaetomorpha”
- AlgaeBarn — “The Complete Guide to Copepods” & copepod culture guides
- Melev’s Reef — Sump articles collection (31 articles on sump design & construction)
- Reef2Reef — Sumps, Refugiums & Filtration forum community threads
- Melev’s Reef — Plumbing articles collection (overflow, return line, closed loop guides)
Related Equipment Guides
The sump houses most of the equipment on the tank. These guides cover what actually goes inside:
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