I just put in 200lbs in my 90g which works out to a 4.5-5" bed...
However, I'm now second-guessing myself, and thinking that a DSB is not a good idea after reading all the DSB maintenance/crash debates. Now's the time for me to pull the sand out if I want, but I can't decide.
If I do pull it out I'd probably go with 2-3" in the display, and a "DSB in a bucket" as opposed to keeping it in the main display.