I should add this: IMO, messing with the sand bed has the potential to cause serious trouble in the tank. About a year ago my tank had a partial crash. The crash followed an attempt by me to thoroughly vacuum clean the sand bed, which in the process stirred up into the water column lots of dendritus and who knows what else. I attribute the partial crash to suspending this junk in the water column, which probably induced a cycle. Adding narsarrius snails would have been a better approach.