Surface skimmers

[Anna94]

What is the purpose of surface and protein skimmers?

 

[alex.walkerrrrr]

They take a film of the top of a (usually established) aquarium, this will aid gas exchange, I highly recommend you get the "Eheim skim 350"

 

[Fresh2o]

Protein skimmers are commonly used in saltwater tanks. A foam is generated in a container via air stone or water pump. Proteins and other substances (surfactants) accumulate in the foam. The excess foam is pushed into a collection cup.
The use of protein skimmers in freshwater is not unheard of, however, it is not very efficient compared to saltwater.