The potential of NSP systems lies in their capacity to be tuned. The makeup and performance of the microbial community, as well as its maintenance, can all be manipulated through relatively simple design changes. The result is filters that have a high capacity for the processing of nutrients. The potential application of biofilter design can be smaller filtration areas, complete elimination of algae, reduction of sedimentation in the swimzone, elimination of plants if desired. All of these improvements result in higher water quality, cleaner pools, and lower maintenance. In very highly tuned systems, the green tints of the water give way to shades of turquoise and blue.
Under the right conditions, Individual microbes soon multiply, and grow into a biofilm. Biofilms are extremely complex. They are organised in multi-species, multi-layer complexes that resemble rain forests in structure, with understories, canopies, and flow channels through which water is drawn by venturi currents. Within the structures, different organisms specialise in different functions, cooperating to form a highly efficient ecosystem which functions much the same as the human digestive system, or a coral reef. The whole complex community is covered by a protective skin that can react to stimuli. The trick about biofilm is to establish it as a healthy Communion in the filter zone, while banishing it from the swimming zone, where it can appear as slime.
Sealed concrete is often used for constructing pools, but caution needs to be taken when building with concrete because some cements can leech undesirable chemicals into the water, which can upset the natural balance of the system. Concrete is rigid and cannot tolerate movement or settlement.
Liners are the most commonly used material for constructing NSPs, especially where the ground is unstable and settlement might occur. Liners are generally (but not always) cheaper to install than concrete, are chemically neutral and do not require as much labour. They can be quickly installed by a small team of skilled technicians.
The best liner for NSPs is synthetic rubber Firestone Pondgard EPDM. It is safe and robust because it stretches, can withstand a good deal of settlement and cracking of the substructure and are relatively resistant to root damage. Firestone Pondgard EPDM can be laid directly onto compacted earth and does not need robust engineering beneath it. It is marginally more expensive per square meter than most other liners, and for more complex designs may require a certain level of skill to install, but they are spliced using a cold vulcanising process, which negates the need for hot welding equipment and makes patching and repairs easy. In Europe, Firestone Pondgard EPDM is the preferred construction material, partly because they re the only material that is flexible and robust enough to accommodate freezing. Firestone Pondgard EPDM generally carries a 30 year guarantee, but can last a lifetime.
PVC and other rigid liners such as LDPE are certainly cheaper per m2, but require technical hot welding equipment and have no inherent flexibility. They do not wear well, especially if exposed to UV, which tends to make them brittle and they tend to tear. They are also difficult to obscure and expensive to repair. PVC has toxic by-products, and they also leach toxins into the water. Only very select PVC liners are rated as compatible for use with sensitive aquatic species and are expensive as a result.
Moulded fiberglass has been used for constructing NSPs. There is a limit to the size of pre-moulded fiberglass pools, and they can be expensive if not made from a preexisting mould. Fiberglass is easier to clean than other materials because it is smooth, but by the same token, it gets slippery when biofilm establishes itself on the bottom and sides of the swimming zone. Fiberglass NSP’s will thus require more frequent maintenance if they are to remain non-slip. Existing fiberglass pools can be converted to NSPs but fiberglass shells will not support the weight of masonry walls inside the shell. When converting fiberglass pools, the filter beds need to be established outside of the shell.
There is a constant stream of new waterproofing products that come into the market, such as polyurethanes and epoxies, but these are not commonly used and care needs to be taken when choosing something untested. Once the filtration beds are installed, it requires a lot of energy to remove again if the product proves unsuitable.