Before I started this quest for reef water aquarium, I was always told to do 3-4" of DSB. So, I started calling for carribean white sand at the fish store and asked for about 150-200lbs of sand. They freaked out and asked me why I wanted that much? I simply told them that it was suggested and I wanted to start my saltwater tank right the first time;hence 3-4" of sand. They, in turn, said it's a bad idea because they are having many problem with there reef tanks. They said that it only causes problem in the later stages because the bottom sand is just trapping bad things. I had called 5-9 different stores and they all said the same. One of them even told me that he has a 100gal reef and he only changes the water once a month because of the lack of sand. However, he said, " if you are creating a plenum, then 3-4" is what you want." So, that's the info that I was told...