Protein skimmer replicates the natural ocean, where waves churn the water and produce foam. Protein (dissolved organic waste) is attracted to the foam bubbles and deposited on the shore. A saltwater skimmer produces fine foam bubbles, which attract proteins from the water. The foam then rises into a waste collection cup.
A nano protein skimmer may be a HOB skimmer (hang on back) or a mini protein skimmer inside the tank or filter compartment. A HOB protein skimmer is good for up to a medium size tank.
Large tanks usually use an in sump protein skimmer. Some extra large tanks use an external protein skimmer that sits beside the sump. The best protein skimmer designs produce tons of air and long contact time to maximize waste removal.
Many high-end skimmers use controllable DC pumps to increase performance.