This category holds two things that solve different problems with the same principle. Three pond filter bags for the discharge of a pond vacuum, and one textile filter sock for borehole and deep well pumps.
The pond bags catch sludge and plant material out of the water a vacuum lifts, so the water can run back into the pond instead of down the drain. The filter sock does the opposite journey: it goes over the pump, in the borehole, and keeps sand away from the intake before it reaches the machine.
Choose by task first, then by grade.
Pond filter bags in 400, 150 and 100 µm · filter sock for deep-well pumps in 50 µm · water return · standard sizes and advice
The three pond grades are coarse, standard and fine. The filter sock is not a fourth pond grade; it is a different product for a different job.
| 400 µm | 150 µm | 100 µm | |
|---|---|---|---|
| Material | polyester screen fabric | polyethylene, monofilament | polyester screen fabric |
| Mesh aperture | 400 µm (380–420) | not documented | 105 µm (99–111) |
| Open screen area | 52 % (49–55) | not documented | 33 % (31–35) |
| Fabric thickness | 285 µm (271–299) | not documented | 120 µm (110–130) |
| Fabric weight | 105 g/m² | 115 ± 20 g/m² | 65 g/m² |
| Best at | leaves, plant debris, coarse sludge | ordinary maintenance | fine sludge and suspended solids |
Two figures in that table do most of the work. Open screen area is the proportion of the fabric made up of openings, and it explains why the coarse bag keeps working while the fine one loads. Fabric thickness explains why the coarse bag copes with a twig and the fine one does not.
Where the row says not documented, no measured value exists for that fabric. We do not fill those gaps with a figure from a neighbouring product.
The 150 is the working grade for a pond in normal condition. The 100 is what you reach for when cleaning has left a haze in the water and you want to catch what is still in suspension.
The trade-off is handling. With 33 per cent open screen area against the 400’s 52 per cent, the fine bag loads faster and drains more slowly. On a pond with a heavy solid load it will need interrupting. That is not a fault; it is what fineness costs.
The 400 is a first stage, not a general-purpose bag. It takes leaves, needles and coarse plant material without closing, which is exactly what a fine bag cannot do.
Its limit is the other side of the same coin: fine sludge and algae residue pass through and return to the pond with the water. If the water is still cloudy after a coarse pass, that is the grade, not the bag.
On a heavily silted pond the sensible answer is both: coarse first, then fine. The solid load is spread across two bags and the fine one stays permeable longer.
The µm values refer to the filter material in use, not to a tested cut-off of the finished bag. What actually stays behind also depends on particle shape, on the load and on the condition of the fabric. A bag that has already built up a sludge layer holds finer material than a fresh one.
This applies to the 50 µm on the filter sock as well. It is a product designation, not a guarantee.
A pond vacuum or a suitable pump moves the sludge and water mixture into the bag. The solids stay behind, the water passes through the fabric and runs back to the pond. You are separating solids during the clean rather than exchanging the whole pond volume.
Two things have to be right for that to work: the bag has to sit where the water can find its way back, and the opening has to match the discharge. Openings of 70 and 105 mm are available.
The filter bag is not water treatment. Dissolved substances, nutrients and bacteria are not removed. WINKLER makes the bags, not the vacuums.
Empty the bag, turn it inside out and rinse with clean water. Rinsing from the inside lifts particles out of the weave instead of driving them in.
As long as fabric, seams, opening and, where fitted, the zip are undamaged, the bag goes back into service. We do not name a number of uses, because soiling, mechanical load and rinsing all determine it.
The bags are made for ordinary garden and ornamental ponds. For koi or swimming ponds with particular hygienic, biological or technical requirements, check first whether and which version suits the system you already have.
Useful details are pond type, degree of soiling, pump output, connection size, the grade you want and how the return is arranged. On a heavily silted pond, a coarse 400 µm first stage followed by a finer one spreads the load across several bags.
Methods, timing and disposal are set out in the guide on removing pond sludge.
Same principle, different problem. The 50 µm filter sock is pulled over a borehole or deep well pump and covers the intake zone, so sand and finer particles meet 2.50 mm of polypropylene needle felt first.
Most well pump filters you will find in search sit after the pump: cartridge housings, inline filters, sand separators, whole-house systems. They protect pipework and irrigation equipment, and they are useful. They do not protect the pump, because the sand has already been through it. Only a filter at the intake does that.
The sock does not fix the cause of a well that produces sand. Outside diameter, overall length, the position of the intake ports and the width of the borehole all have to match the size you choose.
For leaves, plant debris and coarse sludge, the 400 µm bag is the first stage. For ordinary soiling the 150 µm grade suits. Finer suspended solids are caught by the 100 µm grade, usually after a coarser pass.
Not necessarily. A pond pump filter bag can mean a mesh sleeve fitted around a pond pump to keep debris out of the impeller. What you will find here is the bag at the discharge end of a vacuum, which is a different position and a different job.
Yes, as long as they are undamaged. Empty, turn inside out, rinse with clean water, then check fabric, seams, opening and closure.
No. Outside diameter, overall length, position of the intake zone and the situation in the borehole decide. Six sizes cover pump diameters from 74 to 125 mm; for anything else we make it to measure.
Yes. The water passes through the bag while the solids stay behind. The drainage path has to be prepared so the water flows back to the pond. It is not water treatment.
Also a different product. A stationary pond filter sock or media bag sits inside a filter housing and is filled or plumbed in. These bags are fitted to the outlet of a pond vacuum.
The sock keeps sand away from the pump and its intake zone. It does not remove the cause of a persistent sand input. In that case the well itself should be looked at.
Practical examples, selection guidance and further information for choosing products in this category.
Application Updated: August 2026Reading time: approx. 4 minutes Filter the discharge of a pond vacuum: solids stay in the bag, the water runs back to...
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