Protein skimmers having an upright housing including an open topped body with a manually removable foam collection cup for sealing mounting on the body. The foam collection cups encircle a foam collection duct except for a recessed inspection window for exposing an area of the foam collection duct's exterior surface for enabling an aquarist a generally horizontal line of sight to continuously inspect the foam collection duct's interior. The protein skimmers have a canister-like configuration with a front control panel including a main inlet, a main outlet and at least one aspirating pump for circulating an air/water mixture. The protein skimmers include a disperser for dispersing an incoming flow of organic loaded water peripherally downward into a reaction chamber in a substantially uniform manner. The protein skimmers include a washing mechanism for periodically washing their foam collection ducts without having to remove their foam collection cups.