Evolution Aqua Cetus Sieve Gravity Fed Pond Pre-Filter – Mechanical Debris Filter for Koi & Bottom Drain Systems

The Evolution Aqua Cetus Sieve is a professional-grade bow screen pre-filter that removes heavy mechanical waste before water reaches your biological filtration system. Built with a tri-slot 300-micron 316L stainless steel wedge wire screen and a patented Pondflow regulation system, the Cetus Sieve handles up to 18,000 LPH (4,755 US GPH) in either gravity-fed or pump-fed configurations. The one-piece rotationally moulded composite body has no welded joints and no leak points, delivering long-term reliability in demanding koi pond installations. Backed by a 2-year manufacturer warranty. Made in Wigan, UK by Evolution Aqua. Installation options: The Cetus Sieve supports both gravity-fed (Cetus at pond water level, fed by bottom drain, patented Pondflow regulator prevents pump starvation) and pump-fed (Cetus above pond water level, pond pump feeds Cetus via 1.5" inlet, filtered water exits by gravity into downstream filter). Connection sizes differ between the two setups -- see Technical Specifications and FAQ Q6 below before plumbing. 18,000 LPH / 4,755 US GPH Max Flow 300-Micron 316L Tri-Slot Wedge Wire Screen Gravity-Fed or Pump-Fed Patented Pondflow Regulation System One-Piece Moulded -- No Welded Joints 2-Year Manufacturer Warranty SKU: CETUSP | Evolution Aqua | Made in UK What the Cetus Sieve Does In a koi pond system, waste and debris entering the main biological filter cause two problems: they foul the bio-media (reducing bacterial efficiency) and they shorten the intervals between filter cleaning cycles. The Cetus Sieve intercepts this waste upstream -- before it ever reaches your Nexus, EazyPod, K+ pressure filter, or any other biological system. Pond water enters the Cetus through the inlet, passes through the 300-micron 316L wedge wire bow screen, and exits via the outlet to your main filter. Solids that cannot pass through the 300-micron screen accumulate in the large waste collection area at the base, where they are flushed periodically via the 3" waste outlet. Because the screen is a dry screen (waste sits above water level), cleaning requires only a brief hosing-down -- no sponges to squeeze, no media to backwash, no hands-on contact with waste. Technical Specifications Specification Detail SKU CETUSP | Evolution Aqua Cetus Sieve Max Flow Rate 18,000 LPH / 4,755 US GPH Screen 300-micron tri-slot wedge wire, 316L stainless steel -- 100% screen surface coverage Dimensions 33.9"L × 22.6"W × 37.2"H (approx. 860mm × 575mm × 945mm) Installation Gravity-fed or pump-fed (connection sizes differ -- see below) Gravity-Fed Inlet 4" (110mm) Eazy connector Gravity-Fed Outlet 4" straight Eazy connector (verify with EA US distributor) Pump-Fed Inlet 4" to 1.5" Eazy connector Pump-Fed Outlet 4" Eazy connector Waste Outlet 3" (90mm) Eazy connector -- all configurations Flow Regulator Patented Pondflow regulation system (adjustable inlet height, gravity-fed mode) Body Construction One-piece rotationally moulded composite -- no welded joints, no leak points Screen Access Removable 300-micron screen for inspection and deep cleaning Compatible Downstream Filters EazyPod, Nexus, K+ Advanced, any pressurized filter Warranty 2-Year Manufacturer Warranty Origin Made in Wigan, UK (Evolution Aqua) Connection size verification note: The gravity-fed outlet connection size has minor discrepancies between sources (EA manual vs. some retailers). Before purchasing connecting pipework, verify the exact gravity-fed outlet size with Evolution Aqua or call us at (765) 508-4352. The 4" gravity-fed inlet, 3" waste outlet, and 1.5" pump-fed inlet are consistently confirmed across all sources. Gravity-Fed vs. Pump-Fed Installation Gravity-Fed Setup Cetus installed at pond water level in a filter pit Bottom drain gravity-feeds water directly to Cetus inlet (4") Patented Pondflow system adjusts inlet height to compensate for pond water level fluctuations -- pump never starves Filtered water exits outlet to pump chamber, then pump sends water to main biological filter above Install top of Cetus unit 20mm above maximum pond water level Best for: bottom drain ponds with filter pit installations Pump-Fed Setup Cetus installed above pond water level (surface level or elevated) Pond pump draws water from bottom drain or skimmer, feeds Cetus via 1.5" inlet No Pondflow regulator needed (pump provides consistent pressure) Filtered water exits via 4" outlet, gravity-drops into main biological filter below Best for: above-ground installations, pressurized filter systems, skimmer-line pre-filtration Particularly recommended before K+ pressure filters and bead filters to reduce backwashing frequency The 316L Wedge Wire Screen The Cetus Sieve screen is tri-slot wedge wire in 316L marine-grade stainless steel -- the same alloy used in saltwater marine applications. 316L provides superior corrosion resistance vs. standard 304 stainless, essential in an environment exposed to pond water, fish waste, and the slightly acidic conditions of a well-maintained koi pond. The tri-slot profile of the wire creates a self-cleaning tendency as water flows through -- solids tend to sit on the screen surface rather than embedding in the slots, making hose-off cleaning fast and complete. The screen covers 100% of the filtration surface area -- there are no bypass zones where particles can pass around the screen edges. The 300-micron aperture removes particles down to 0.3mm -- significantly smaller than the debris that typically fouls biological filter media. This means the bio-media in your downstream filter (K1 Micro, K+ Media, filter pads) receives only genuinely fine particles, maximizing biological surface efficiency and reducing cleaning frequency dramatically. Patented Pondflow Regulation System For gravity-fed installations, pond water levels fluctuate continuously -- through evaporation, rainfall, and normal pump operation. Traditional static-inlet sieves respond to falling water levels by reducing flow to the pump, potentially starving it and damaging the motor. Evolution Aqua's patented Pondflow regulation system uses an adjustable inlet height that automatically compensates for changing water levels, maintaining a consistent water supply to the pump regardless of minor level fluctuations. This is a genuine engineering advantage for unattended pond systems and is one of the primary reasons the Cetus Sieve commands a premium over simpler sieve pre-filters. Compatible Downstream Filters Evolution Aqua EazyPod Complete -- koi ponds up to 2,640 US gal; pair with Cetus for extended maintenance intervals and superior water quality Evolution Aqua Nexus -- professional koi filtration; Cetus as pre-filter dramatically reduces Nexus waste valve cycling frequency Evolution Aqua K+ Advanced pressure filters -- Evolution Aqua specifically recommends pre-filtering all pressurized filters with a Cetus to reduce backwashing Any pressurized bead or media filter -- the Cetus is compatible with all biological and pressurized filter systems Frequently Asked Questions Why is the Cetus Sieve considered the best pre-filter for koi ponds? Three things distinguish the Cetus Sieve from simpler sieve pre-filters: 316L marine-grade wedge wire screen: Tri-slot profile covering 100% of the surface area -- no bypass zones. 300-micron aperture captures particles a standard drum screen misses. 316L alloy resists corrosion in pond chemistry better than 304 stainless or plastic mesh alternatives. Patented Pondflow regulation system: Automatically adjusts the inlet height in gravity-fed setups to compensate for pond water level changes, preventing pump starvation without manual adjustment. One-piece rotationally moulded body: No welded joints means no potential leak points. The robust composite construction withstands the pressure of being buried in a filter pit and the thermal cycling of outdoor installation. How does the Pondflow regulation system work? Evolution Aqua's patented Pondflow regulation system is specifically designed for gravity-fed installations where the Cetus Sieve is installed at pond water level, fed by a bottom drain. Pond water levels fluctuate throughout the day -- evaporation, rain, and pump operation all affect the level. A fixed-height inlet would cause reduced flow (and potential pump starvation) when the water level drops below the inlet. The Pondflow system uses a variable-height inlet that automatically adjusts to maintain consistent flow into the Cetus even as water levels change. This ensures your downstream pump always has adequate water volume and protects the pump from running dry during unattended operation. For pump-fed installations, the Pondflow system is not needed -- the pump provides consistent pressure regardless of water level. What is the maximum flow rate? The Cetus Sieve supports a maximum flow rate of 18,000 LPH (4,755 US GPH) in both gravity-fed and pump-fed configurations. For context, a typical koi pond turnover target of once every 2 hours means: A 10,000L (2,640 US gal) koi pond requires ~5,000 LPH for 2-hour turnover -- well within Cetus capacity A 30,000L (7,925 US gal) pond requires ~15,000 LPH -- still within the 18,000 LPH maximum The Cetus is sized to handle all but the largest residential koi ponds on a single unit. For ponds exceeding ~36,000 litres requiring higher flow rates, two Cetus units in parallel can be installed. Is the Cetus Sieve easy to clean? Maintenance is faster and cleaner than any sponge-based pre-filter. Because debris collects on a dry screen surface above the water line, cleaning involves three steps: Spray the 300-micron screen with a garden hose -- waste rinses off in seconds Open the 3" waste outlet valve to flush accumulated debris from the waste collection sump For periodic deep cleaning, remove the 300-micron screen from the unit, rinse thoroughly, and reinstall No sponges to squeeze, no beads to backwash, no reaching into the filter. Most users clean the Cetus screen every 2--7 days depending on fish load and debris levels. Compared to cleaning a biological filter directly, Cetus maintenance takes under 5 minutes. How does the Cetus Sieve improve pond oxygenation? As water moves through the 300-micron wedge wire screen at flow velocity, it undergoes gas exchange -- atmospheric oxygen dissolves into the thin-film water layer crossing the screen, while dissolved carbon dioxide is released. This provides a measurable oxygenation benefit, particularly in warm summer months when dissolved oxygen levels in koi ponds can drop to stressful levels for fish. Evolution Aqua describes this as: "As the water is moved quickly through the sieve, oxygen enters the flow increasing vital levels and improving water quality." This aeration benefit is secondary to the Cetus's primary mechanical filtration function, but it is a genuine operational advantage vs. closed-system pre-filters that provide no gas exchange. What are the inlet, outlet, and waste connection sizes? Connection sizes differ between gravity-fed and pump-fed installation modes. Consult the EA manual or call us at (765) 508-4352 to confirm for your specific setup before purchasing connecting pipework: Connection Gravity-Fed Pump-Fed Inlet 4" (110mm) Eazy connector 4" to 1.5" Eazy connector Outlet 4" straight Eazy connector 4" Eazy connector Waste 3" (90mm) Eazy connector 3" (90mm) Eazy connector All Eazy connectors for the inlet, outlet, and waste port ship pre-fitted to the unit for faster initial installation. The 3" 90-degree waste Eazy connector is supplied separately for user fitting. Evolution Aqua Cetus Sieve (CETUSP): 300-micron 316L tri-slot wedge wire, 18,000 LPH (4,755 GPH), gravity-fed or pump-fed, one-piece rotationally moulded body, patented Pondflow system, 2-year warranty. Dimensions: 33.9" x 22.6" x 37.2". Made in Wigan, UK. Questions about Cetus installation, filter pit dimensions, or pairing with EazyPod or Nexus? Call or text (765) 508-4352 -- Monday through Friday, 9 AM to 5 PM EST.