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Overview
Standalone 20-litre solar pond filter box with four sealed filtration chambers. Submersible — drops straight into your pond. Pair with any 300-1500 LPH pump (sold separately) or use as a drop-in replacement for an existing kit.
20 Litre Solar Pond Filter Box — Submersible 4-Chamber Filtration
The PowerBee SPF-20 is a standalone 20-litre submersible pond filter box with four sealed filtration chambers. Drop it in your pond, connect any 300-1500 LPH pump (solar or mains), and water flows through mechanical, biological, and polishing media before returning crystal clear. Ideal for ponds up to 1,500 litres (1,000L with fish). UK stock, free delivery.
Bring Your Own Pump — Or Replace a Worn-Out Box
This is the filter box on its own — no pump, no panel, no hosing. Bought separately so you can pair it with the pump you already own, upgrade the box on an existing kit, or build a custom solar filtration setup. If you'd prefer the complete solution, look at our Solar Pond Filter Kit (700 LPH pump + 12W panel + this box) or the 1400 LPH MPPT Battery Kit for larger ponds.
Four Filtration Chambers — Mechanical, Biological & Polishing
Most cheap pond filter boxes have a single chamber stuffed with one type of media — water shoots through unfiltered. The SPF-20 splits filtration into four sealed chambers, forcing water through each stage in sequence:
Chamber 1 — Coarse mechanical: sponge or filter pad traps leaves, debris and large particles before they clog finer media
Chamber 2 — Fine mechanical: traps suspended sediment, dead algae, fine particulate
Chamber 3 — Biological: bio-balls or ceramic media host beneficial bacteria that break down ammonia and nitrites
Chamber 4 — Polishing & outlet: final clarification before water returns to the pond, optionally via a fountain head
The four-chamber layout extends time between cleans, protects the biological colony when you rinse the mechanical stages, and gives noticeably clearer water than single-chamber buckets.
Submersible — No Priming, No Pond-Edge Plumbing
Unlike gravity-fed pond filters that sit beside the pond and need careful levelling, syphon priming, and exposed hosing, the SPF-20 sits in the water. Connect your pump inside the box, drop the assembly in, and run a single cable out to the bank. The box is hidden under the waterline, fountain heads sit on the lid, and the whole installation looks like a normal pond fountain.
What's in the Box
SPF-20 filter box (20 litres, 372 × 330 × 185mm)
Removable lid with quad-chamber moulding and fountain-head positions
Internal media baskets (4)
Not included: pump, solar panel, cable, hosing, filter media. The box is sold as a standalone replacement or DIY component. If you need the complete working setup, choose the Solar Pond Filter Kit instead.
Pond Size Guide
Up to 750L (no fish): SPF-20 is overkill — consider the smaller PowerBee Eco Filter Box (SPF-6.5/SPF-10)
750-1,500L (no fish): SPF-20 is the right size, paired with a 300-700 LPH pump
1,000L with fish or heavy organic load: SPF-20 with a 700-1500 LPH pump and a 5W UV clarifier add-on
1,500L+ or koi: step up to the SE2000-SPF20-KIT (1400 LPH + battery + same 20L box)
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The SPF-20 is designed to sit submerged on the pond bed or shallow shelf. Total install time is around 15-20 minutes once you've chosen your pump.
Step 1 — Choose Your Pump
The SPF-20 accepts any submersible pump rated 300-1,500 LPH. For solar use, our 700 LPH 12W solar pump (sold separately) is the matched pairing. For mains use, any pond pump with a similar flow range will work. The pump sits inside chamber 3 of the box.
Step 2 — Load the Filter Media
If the box did not arrive pre-loaded, fit media in chamber order:
Chamber 1 — coarse sponge or filter pad
Chamber 2 — fine sponge or filter wool
Chamber 3 — bio-balls or ceramic noodles around the pump body
Chamber 4 — polishing pad (optional)
Replacement media is available from any pond shop in standard sizes.
Step 3 — Connect Pump & Cabling
Place the pump in chamber 3 with the outlet aligned to the lid's fountain-head opening (or hose port)
Run the pump cable up through the lid notch
Fit the lid firmly — it should click into place on all four sides
Run the cable out of the pond to your power source (solar panel or mains transformer), keeping the connection point above the waterline
Step 4 — Position in the Pond
Lower the box gently into the pond — the moulded feet should sit flat on the pond floor or shelf
Check the lid is just below the waterline (so the fountain heads sit at the surface)
If using a fountain head, fit it to the lid post; if using a hose return, attach the hose to the lid outlet and route to your waterfall or feature
Step 5 — First Run & Cycling
Switch on the pump. Water should circulate within seconds, with output appearing through the fountain head or hose. If you have fish, expect 4-6 weeks for the biological filtration to fully cycle (beneficial bacteria colonise the bio-media gradually).
Maintenance
Weekly: visual check that flow is still strong
Monthly (or when flow drops): lift the box, remove the lid, rinse chambers 1 and 2 (mechanical) in a bucket of pond water — never tap water, which kills bacteria
Seasonally: rinse chamber 3 (biological) gently in pond water — replace media every 12-18 months
Winter: in hard frosts, lift the box and pump indoors. The empty box can stay submerged.
A pond filter has one job: take cloudy, organic-laden pond water and return it clear and oxygenated. The SPF-20 does this in four sequential stages inside a single submerged box, with your pump providing the flow.
Stage 1 — Mechanical Filtration (Coarse)
Pond water is drawn into the box through inlet slots. The first chamber holds a coarse sponge or filter pad that traps large debris — fallen leaves, fish waste, twigs, dead algae. This stage protects the finer media downstream from clogging too fast.
Stage 2 — Mechanical Filtration (Fine)
Water passes into chamber 2 with a finer sponge or filter wool. Suspended sediment, fine particulate, and microscopic debris are caught here. By the time water leaves this chamber it is visually clear — but biologically still loaded.
Stage 3 — Biological Filtration
Chamber 3 holds bio-media (bio-balls, ceramic noodles or porous plastic) with vast surface area. Beneficial bacteria — Nitrosomonas and Nitrobacter — colonise the media and convert toxic ammonia (from fish waste and rotting matter) first to nitrite, then to harmless nitrate. This is the stage that keeps fish alive and pond water healthy. Your pump also sits in this chamber.
Stage 4 — Polishing & Return
The final chamber gives water a last polish through a fine pad and routes it out through the lid — either up through a fountain head for surface aeration, or through a hose to a waterfall, stream or pond return. The aerated return adds dissolved oxygen, which fish, plants, and beneficial bacteria all need to thrive.
Why Submersible Beats Gravity-Fed
Traditional pond filter boxes sit beside the pond and rely on gravity. Water has to be pumped up into them, then drains back via gravity. This means: an exposed unit on the bank, longer hose runs, syphon priming when the pump restarts, and the filter visible from every angle. The SPF-20 lives under the waterline. The only thing visible above the surface is the fountain head. The pump pressurises a closed system, so there's no priming, no airlocks, and nothing on display.
Why a 4-Chamber Box Outperforms Single-Chamber Buckets
A single-chamber filter mixes all media types together. When the coarse sponge clogs, water finds the path of least resistance and bypasses the bio-media — meaning your biological filtration silently fails. The SPF-20's sealed chambers force water through every stage in sequence, every time. When you rinse the mechanical sponges (chambers 1 & 2), you don't disturb the bacteria living in chamber 3. The biology stays alive, the water stays clear, and the pond stays healthy.
