maybe he is an expert to this. cos he does alot of researches. As we know, DSB isn't the only filtration way. There are also mechanical filtration. Think they have done alot of research, based on their own experience, advises from the expert locally, overseas. We wouldn't know. No need change water? Underwater world for instance, dun think they have much of a water change(i maybe wrong) they very much rely on those heavily invested equipments and filtration to keep their LS healthy.