In Germany, fears that disposed of waste saltwater were an environmental pollutant nearly legislated the marine hobby out of existance a couple decades ago. Tunze and other European companies responded by developing filters that are essentially miniature sewage treatment plants and all components working together allow the aquarium to be successfully maintained without water changes. Besides that, water changes can actually be detrimental as they do tend to result in osmotic changes that more sensitive animals cannot endure. I have since changed my approach slightly and change 10% per month. I do this because I found that the trace elements are depleted and additives tend to shift the ionic equilibrium, especially many calcium additives. I use supplements at half the recommended dose and only what is essential. It is not any one component that makes this possible, it is a skimmer, bio reactor, mechanical filter, carbon, phosphate remover and a low population density all combined that make this possible and to really keep to no water changes one would need a calcium reactor and sparing use of supplements for trace elements to keep the ionic balance more or less in check.