A protein skimmer is a piece of aquarium equipment that is primarily used in saltwater/marine aquariums. They are used to help remove dissolved organic compounds (DOC’s) and other harmful substances from the water column. If these are not removed, they can add to the biological load of the aquarium which would result in higher nitrate levels. Skimmers do NOT remove nitrates (unless they are bound to a carbon source, such as vodka/vinegar), however they remove organic compounds from the aquarium water column that can later become nitrates if they are allowed to be digested by the beneficial bacteria within the filter/live rock.
Protein skimmers remove these dissolved organic compounds from the water column using thousands of tiny air bubbles, which are collected by a collection cup.
A basic protein skimmer will use a pump and a venturi tube attached to the pump. The venturi will pull in atmospheric air, forcing it into the pump. Instead of a ‘normal’ impeller which usually has 4 fins, protein skimmer pumps usually have ‘needle wheel’ impellers or something similar, which have multiple, thinner fins. This is more efficient in breaking up the atmospheric air pulled in by the venturi, as the impeller will ‘blast’ the air being pulled in, creating the thousands of microbubbles you see moving up through the centre of the protein skimmer.
As the bubbles rise  through the organic-laden water in the centre of your protein skimmer, the electrically charged protein molecules (DOC’s) are attracted to the water/air surface of the bubble. So these protein molecules will adhere to the bubble, rising through the water column to the top of the protein skimmer, where they will then be pushed out the ‘neck’ of the protein skimmer and into the collection cup, effectively removing the organic waste. 

Find our range of protein skimmers here. 

Can I have a protein skimmer on a tropical tank?

You can indeed have a protein skimmer on a tropical set up, however due to the different chemical compounds which differentiate salt water aquariums from tropical aquariums; they are less effective in a tropical set-up. Protein skimmers work by creating bubbles or foam which large waste particles can attach and be removed, however you will find that non-salt water does not foam or bubble as successfully as salt.
Due to this, the skimmer will not be effective at removing particulates. There are however, surface skimmers designed for tropical aquariums which work to skim the surface. You can find our surface skimmers here.