Protein skimmers for salt tanks, mimic the sea shore. Have you ever been to the beach and seen the foam near the shore? Protein Skimmers mimic this action by bubbling into a column and allowing the foam to be captured. I foam is broken down protein from the fish and their shit being reused in the natural salt environment.its used in fresh and salt aquariums. it adds mad oxygen to water. Could it have any practical usage in hydro grow systems?