Aquatic Filter Foam Guide

Pond and tank filters are essential for keeping water clear and clean for fish and other organisms, helping to promote a balanced biological ecosystem. They remove waste and debris from the water to maintain a healthy pond or tank, and there are several types – mechanical and biological systems – each with different levels of maintenance and efficiency.

How filter foam works

These filters are aided by a polyurethane foam (usually with a polyester polyol or polyether) that undergoes a reticulation process to produce an open-cell foam with a dense, complex cell structure. This creates a foam resistant to material breakdown and oxidation, making it well suited to a filtration system.

Mechanical filtration

Reticulated polyether aquatic foam plays a crucial role in mechanical filters, considered by many the most popular and effective method of water filtration. It sieves out solid waste, algae, dirt and grit as water is drawn through it by a submersed pump. Run permanently or occasionally, these filters are cost-effective and available in a range of sizes for indoor tanks and outdoor ponds. The right size is determined not by the size of the pond or tank but by the number of fish and organisms, so tanks with only a few fish may not strictly require a filter, though one is still recommended. Being chemically and structurally stable underwater for long periods, and resistant to fresh and salt water, bacteria, humidity, oils and lubricants, reticulated foam helps break down bio-waste, protects the pump from debris, reduces algae-promoting nutrients, and traps fine particles. Our guide to pool filter foams covers related uses.

Biological filtration

Mechanical filtration is most appropriate for smaller environments such as tanks and offers basic support for cleanliness and fish health. However, biological filtration should also be considered for outdoor ponds and larger aquatic environments, as a lack of it is the number one cause of fish death. In biological systems, reticulated polyether foam acts as a bacterial carrier, improving the active surface and efficiency of the bioreactor – the natural organisms present in the tank. It's worth understanding the difference between open-cell and closed-cell foam here, as filtration relies on an open-cell structure.

eFoam supplies high-quality aquatic solutions for individual and commercial tanks and ponds, and has been a leading adviser on foam products for several decades. To discuss your aquatic foam requirements – mechanical, biological or both – please contact us.

Frequently asked questions

What foam is used in aquatic filters?

A reticulated polyether polyurethane foam, with a dense, complex open-cell structure created by a reticulation process. It resists material breakdown and oxidation, making it well suited to a filtration system, and it stays chemically and structurally stable underwater for long periods.

How does mechanical filtration foam work?

Reticulated polyether foam sieves out solid waste, algae, dirt and grit as water is drawn through it by a submersed pump. Its dense structure also traps smaller particles that are hard to see, helps protect the pump from debris, and reduces the nutrients that promote algae growth.

Do I need a biological filter too?

For outdoor ponds and larger aquatic environments, yes – a lack of biological filtration is a leading cause of fish death. In biological systems, reticulated polyether foam acts as a bacterial carrier, improving the active surface and efficiency of the bioreactor.