sera marin Protein Skimmer PS 400 HO A protein skimmer is indispensable in a saltwater aquarium. It regulates the removal of proteins, phosphates and other substances, prevents algae growth and increases the oxygen level. In addition to the existing marin range, sera has developed two powerful protein skimmers that produce tiny bubbles and therefore ensure excellent skimming performance. Being a hang-on version, the sera marin Protein Skimmer 400 HO is ideal for smaller aquariums up to 400 liters that are not equipped with a separate filter tank. It is easy to adjust and ensures highly effective protein skimming in saltwater aquariums.