Fish Mate 4000G-UV Gravity Pond Filter – 8W UV

Fish Mate 4000G-UV gravity pond filter

The Fish Mate 4000G-UV is a pump-fed, gravity-return pond filter with an 8W ultraviolet lamp, mechanical foam filtration and SUPRA biological media. This listing is for the UK 4000G-UV, manufacturer reference 336. Its maximum permitted water flow is 2,500 litres per hour. A suitable pond pump is separate.

Choose this type of filter when you can position the box so the filtered water returns downhill to the pond. Plan the whole water route before choosing your pump: the pump pushes water into the filter, but the outlet arrangement must let the water drain away freely. It is important to distinguish a gravity-return box from a pressure filter when laying out a pond.

Technical details and pond capacity

Detail	UK 4000G-UV specification
Manufacturer model	4000G-UV, reference 336
UV lamp	8W; Fish Mate replacement reference 329
Maximum filter flow	2,500 litres per hour
Water return	Gravity return; unrestricted downhill outlet route
Filtration	Foams and SUPRA biological medium, with UV clarification
Nominal maximum pond size	4,000 litres; fish stocking and site conditions reduce this figure
Shaded pond with plants and light fish stocking	Manufacturer selection chart: up to 2,000 litres at its stated stocking basis

The selection chart’s light-stocking basis is up to 25cm of fish per 500 litres, with water plants and full shade. The 4,000-litre nominal maximum is therefore not a recommendation for every 4,000-litre fish pond. Koi, heavier feeding and a sunny site call for a different capacity assessment. Compare your actual pond conditions with the selection chart before ordering.

Understand what each stage does

A pond filter has several jobs. Capturing suspended debris helps keep the water looking tidy; a biological stage supports the processing of fish waste as the system matures. UV clarification addresses suspended algae associated with green water. These functions complement one another, and none removes the need to maintain the pond or check water quality.

Water that looks clear can still have a water-quality problem. Use a suitable pond water test kit to monitor the pond, particularly when you change the filter, increase the fish stock or alter feeding. Record results over time so you can distinguish a stable system from one that is still settling in.

Choose the pump by delivered flow

The manual gives a guide flow of approximately half the pond volume each hour, within the filter’s maximum. Above 1,250 litres per hour, both outlets must be used. The highest flow through this UK model remains 2,500 litres per hour. These are filter limits, rather than a statement that any pump with a similar number on the box will be suitable.

A pump’s maximum output is normally quoted before the losses in a real installation. Hose length, height difference, fittings and the pump’s own flow curve matter. Work out the route to the proposed filter position, then compare the pump’s delivered-flow information. Keep enough access around the filter to see whether water is returning properly after cleaning or an adjustment.

Plan the gravity return and hose connections

Measure the available position at the pond edge and the return route before buying hose. Think about where an outlet will discharge, whether the hose can remain supported and whether a bend would leave water trapped. Avoid a layout that relies on water being pushed uphill after it has left a gravity-return box.

Compare our standard flexible pond hose options against the actual filter and pump connections. Hose dimensions, the fitting shape and the clip all need to agree. Do not trim a stepped connection or buy an adapter from the model name alone: check the supplied fitting and its instructions first.

Keep routine servicing practical

A good filter position makes maintenance easier. Leave room to lift the lid, place a bucket nearby and inspect the hose connections. Keep the access route clear so servicing does not require you to move a heavy planter or dismantle a decorative surround. Notice how the water behaves when the filter is clean; that gives you a useful baseline for later checks.

Isolate the pump and UV supply before opening the filter. Follow the supplied care instructions when cleaning its media. Keeping a simple maintenance record helps you recognise when a foam is repeatedly becoming blocked, when a lamp was fitted and whether a change in the pond coincided with a change in the filter’s performance.

Order replacement parts by model and reference

Keep the model label and the manual with your pond-equipment records. Before buying a replacement lamp, compare the stated lamp reference, physical connection and electrical rating. This unit uses the Fish Mate 8W lamp reference 329. Do not choose a lamp solely because another filter also has the number 4000 in its name.

Our pond UV bulb range is a useful place to compare lamp formats, but confirm the exact compatibility before selecting a substitute. A correctly identified part is more useful than a similar-looking tube. Inspect seals, fittings and the enclosure during routine servicing, and keep electrical installation and repairs within the manufacturer’s requirements.

Compare a different installation arrangement

If your proposed return route does not suit a gravity-return filter, compare the Oase BioPress 4000 pressure filter. It has a different water-path arrangement and different model-specific limits. It is an alternative to assess for your installation, rather than an interchangeable part or a promise of the same fish-pond capacity.

Before placing an order, check the pond volume, fish stock, filter location, pump delivery and space for servicing together. The best choice is the one whose complete installation suits those requirements. This page supplies the UK 4000G-UV filter; a pump, hose and separate accessories should be selected for the actual layout.