Mostly they are exaggerations and lies, but there are a few real cases. They usually have well established deep sand beds of 6 to 8 inches or more and they had to do water changes usually for up to several years before the sand beds became developed well enough to do all the denitrification. Even then, most of them, if they had any substantial amount of coral, had to do supplemental inputs for calcium. Other than that they were just typically doing water top offs after the tank was established for one or two years. Even then they did it to prove a point, they do not recommend it regularly. It is a research tool not a method of operation that is promoted for general reef tank persons. Typically they had/have just token loads of fish, corals and invertebrates. Most of them were very hard pressed before they would even admit to calcium supplementation with Kalkwasser as ATO water. These people were researchers not aquarium trade professionals like Calfo, Fenner, Riddle, or Joshi etc..