Some skimmer manufacturers provide these tanks as an option for their products. If the layer gets thinner, a suction skimmer may need sensors and controls to shut off the motor to prevent the ingestion of a large amount of water, particularly if there is turbulence in the reservoir. Also, water and oil tend to emulsify due to churning as they go through the pump. The most important liquid parameters affecting media selection are temperature range, pH and the presence of solvents. Most skimmer manufacturers offer polymer media, some also offer stainless steel.
Cost is a consideration as any medium has to be replaced from time to time.
In tube and mop skimmers, the user is restricted to polymer because of the medium's shape. Belt skimmers can use both media types, and depending on design, may allow easy switching if one proves unsuitable. Some designs allow a change of media type without changing pulleys. Others require different pulleys for different media, making modifications more difficult. Polymers are good for applications where abrasive particles are present, or when physical abuse can occur.