Natural Pool and Swimming Pond: Technology and Filtration
Natural pools and swimming ponds clean their water biologically rather than chemically – entirely without chlorine. This introductory guide explains how the regeneration zone, filter technology and circulation work together, and how much maintenance you should realistically plan for.
Natural pool or swimming pond: the distinction
Both construction methods do without chemical disinfection and instead rely on a biological balance. The difference lies mainly in the proportion of technology and in the appearance of the water. A swimming pond works largely close to nature: a generous, planted regeneration zone handles the cleaning, while circulation is low or absent altogether. The water looks alive and slightly greenish. A natural pool (sometimes called a Living Pool) shifts the cleaning more towards technology – pump, filter, skimmer and often a separate biofilter. The result is clearer, pool-like water with a smaller or completely separate planting zone.
The FLL guideline for swimming and bathing ponds groups both forms into several types that differ in their degree of technical support – from the purely biologically operating swimming pond to the largely technically managed natural pool. For the planning, you should bring in a specialist company that focuses on near-natural pools, as sizing and planting depend heavily on the location.
| Feature | Swimming pond | Natural pool |
|---|---|---|
| Regeneration area | large, often similar to the swimming area | smaller, frequently replaced by a technical biofilter |
| Use of technology | low to none | higher: pump, filter, skimmer |
| Water appearance | near-natural, slightly greenish, pond character | clear, pool-like |
| Planting in the swimming area | common | mostly separate or not visible |
| Maintenance character | seasonal, horticultural | regular, technically oriented |
Structure of the regeneration zone
The regeneration zone is the biological heart of every near-natural installation. It usually consists of a mineral substrate (gravel, chippings or special filter substrates) through which the water flows slowly. On the enormous surface of the grains, a biofilm of bacteria settles that breaks down organic load and converts nitrogen compounds. The marsh and aquatic plants used additionally draw nutrients out of the water and shade the substrate.
In the classic swimming pond this zone is laid out over a wide area and separated from the swimming area by a dividing wall below the water surface or a gravel berm, so that you can swim without obstruction. In the natural pool the function is often shifted into a compact, flow-through biofilter and the visible planting is reduced. In both cases it is decisive that the water actually flows through the cleaning stage and does not merely pass by on the surface – otherwise the biological effect fails to materialise.
Filter technology and circulation
Even without chemicals, an orderly water flow is needed. The usual arrangement is a chain of mechanical pre-separation (skimmer and sieve or brush filter against leaves and suspended solids), a gently conveying circulation pump and the biological stage (regeneration zone or biofilter). A phosphate filter frequently supplements the chain, since phosphate is the growth-limiting nutrient for algae.
Circulation is deliberately gentler than in a chlorinated pool: the aim is complete but slow circulation that does not disturb the biological balance. Energy-saving, variable-speed pumps are clearly advantageous here, because they run economically over long operating times. The pipework is usually made of seawater-resistant PVC-U, and on the circulation line in d50 (DN 40) or d63 (DN 50) depending on the volume. A main drain collects sediment from the pool floor, while the skimmer collects surface contamination. UV units are used only very sparingly, as they can also harm beneficial microorganisms.
Limiting nutrient input
Clear water in a natural pool is above all a question of a low nutrient level. The less phosphate and nitrogen enter the pool, the fewer algae can form. The target value for phosphate is very low, in the microgram-per-litre range – well below what many people would notice.
Typical sources of input and countermeasures:
- Leaves and pollen: use the skimmer consistently, stretch a leaf-protection net in autumn, vacuum off sediment.
- Bathers: shower before bathing; sun cream, sweat and skin flakes introduce nutrients.
- Surroundings: do not apply lawn or bed fertiliser near the pool; keep grass clippings and soil away.
- Fill water: check fill water that is already nutrient- or phosphate-laden in advance and, if necessary, feed it in through a phosphate filter.
In addition, phosphate-binding substrates or filter materials permanently bind excess phosphate. In this way the algae are literally deprived of their food.
Maintenance effort over the year
Near-natural pools are low-maintenance, but not maintenance-free – a realistic picture is more important than the advertising promise of a maintenance-free pond. The effort shifts from dosing chemicals towards regular observation and horticultural care.
- Spring: put the technology into operation, clean the filters, vacuum off settled sediment. Filamentous algae are normal now, as long as the biological balance is building up again.
- Summer: check the skimmer and pre-filter, keep the surface and floor clean, keep an eye on the water values, thin out plants if needed.
- Autumn: stretch a leaf net, cut back plants, remove sediment, clean the filter thoroughly.
- Winter: the pool usually stays filled; however, drain frost-sensitive technology and pipes or move them to a frost-free place.
Expect a new installation to take the first one to two years to settle in. If you keep nutrient input low and stick to the simple routines, you will usually have stably clear water afterwards with manageable effort.
Bill of materials
Example – please verify with a specialist. Parts and quantities depend on the installation; sizes shown are examples.
| Component | Size | Art. No. | KLN No. | Qty |
|---|---|---|---|---|
| Regeneration zone (planted substrate) | – | – | – | Biological cleaning stage; area, depending on the construction method, roughly equal to the swimming zone (swimming pond) or smaller (natural pool). |
| Biofilter / phosphate filter | – | – | – | Technical cleaning stage with substrate for biofilm and for phosphate binding. |
| Energy-saving circulation pump | – | – | – | Delivers gently over long run times; look for low consumption and resistance to lake/natural water. |
| Skimmer and main drain | – | – | – | Mechanical pre-separation of floating debris at the surface and sediment at the pool bottom. |
FAQ
What is the difference between a natural pool and a swimming pond?
A swimming pond cleans in a near-natural way via a large planted regeneration zone with little technology. A natural pool shifts the cleaning more towards technology such as a pump, filter and biofilter, and thereby delivers clearer, pool-like water.
Does a natural pool really need no chlorine?
Yes. The cleaning is handled by bacteria in the substrate, plants and the filter technology. Doing without disinfectants does, however, require that nutrient input is kept consistently low.
How much area does the regeneration zone need?
In the classic swimming pond, the regeneration area is often roughly as large as the swimming area. In the natural pool it is smaller or is replaced by a technical biofilter. The exact sizing depends on the location and belongs in expert hands.
Why is phosphate so important?
Phosphate is the limiting nutrient for algae. If it stays very low, the algae lack food and the water stays clear. That is why skimmers, phosphate filters and a low nutrient input are central.
Is a natural pool frost-proof in winter?
The pool usually stays filled and withstands frost. However, you should drain frost-sensitive pumps, filters and pipes in the technical area in good time or move them to a frost-free place.
This guide provides general technical orientation and does not replace professional planning. Safety-, electrical- and permit-relevant work must be carried out by qualified specialists.
