I had a DSB in my old 30 gallon and a number of events may have led to a crash and the subsequent removal of my DSB.
Fall 2002 - I originally added a DSB (around 4" in my 30 long).
April 2003 - Ice STorm knocks out power for 3 days with outdoor temps in single numbers and indoor temps in the 50's. I also had no water movement. Approximately 50-70% of my corals died or were dying. I removed the dead snails, fish and corals.
September 2003 - I had a major outbreak of red slime algae, so I decide to clean up the top of the DSB and actually disturbed the sand a bit. A day or two later....boom....major death. I lost two fish and just about the remainder of my corals. The ones that remained alive were all shriveled up.
I worked with Tom at TRS and did a bunch of 50-75% water changes with no real luck (new fish and snails would just die even though parameters were OK). We eventually assumed that it was a DSB crash. Tom thought that the April blackout may have caused the death of most of the organisms that were responsible for turning over my sand which in turn led to a buildup of bad gases in my DSB. Then when I stirred up the bed in September, I released these gases and pretty much killed everything.
So I removed the DSB and went with an aragonite base of about 1" and did a complete water change. The corals I had remaining (a couple of ricordia, a scolymia, a frogspawn and devil's finger immediately came back to life. I was able to keep snails and fish again and the rest is history.
When I removed the DSB, I basically used two 20 gallon rubbermaid containers to place my LR and corals. Then drained the tank and emptied the sand with a plastic cup into a contractors bag. I then hosed out the tank and refilled it with the new water and replaced the rock. I did not add the aragonite right away, I waited a few weeks.
Hope that helped.