DSR stands for "Dutch Synthetic Reefing". This is a way of keeping a mixed reef aquarium successful without water changes. The DSR Method was developed by "Glenn Fong" as a problem solving tool for his own 1500 liter mixed reef aquarium. No water changes and controlling essential water parameters are the basics of the DSR Method.
Read more about Glenn's experiences here:
Jan2014, Publication in Reef Hobbyist magazine (California, USA) "A FLOURISHING DUTCH SYNTHETIC REEF"
https://issuu.com/.../7d3d5bcad324d3edc08e40738e663554-q1/41