A surface skimmer is a really useful addition to any external filter

A surface skimmer (JBL TopClean II) is a really useful addition to any external filter, as it keeps the water surface clean and ensures the water above the surface is ideally enriched with oxygen.

Surface Skimmer - Fluval USA

Is A Surface Skimmer Beneficial For A Freshwater Aquarium? – TRUVU Aquariums

Reef Equipment - Pacific East Aquaculture

Oberflächenabsauger Aquarium

AMK Surface Skimmers For Aquascaping with Oase Canister Filters, Azoo Hydra Aquatics Stainless Oase

The easy-to-use SwimSkim is a powerful surface skimmer that floats along the surface of ponds up to 270 ft2 removing debris. The compact SwimSkim easily integrates into an existing pond, automatically adapting to any water level (from 16 in. water depth). The accumulated debris can be easily removed using the leaf basket. Integrated aerator oxygenates your pond while skimming the surface.

Oase SwimSkim Pond Skimmer

Coral vue octopus with external 1000 pump 378.5lbrgt; This design also allows for easy removal of the pump for cleaning and maintenance They are built with high quality acrylicThe bh-1000 is a unique design hang on back skimmer in that the pump is mounted external and under the actual skimmer body allowing for much less room needed behind the aquarium. Also by placing the pump outside the skimmer and the aquarium there is no heat exchanged to the water.