"Marx" <email@example.com> wrote in message news:firstname.lastname@example.org... > I have one question - why fine sand doesn't flow all over the tank, when > there are many pumps? I was told it does to some extend. But the finest particles are glued together to make bigger ones by bacteria on them... It takes a couple days to a week to settle the finest particles on the bottom due to the bacteria activity. I did not have DSB in the main tank myself so I am interested in this question as well. A lot of people have DSB in the refugium, so the water turbulency is not so great and they would not tell us.