I disagree with the above statement. You need critters in the DSB
or it will crash. There are some things you want to avoid such as sand sifting stars. Nassarius snails,cerith snails, conchs, all types of pods
, bristle worms, even a cucumber (if you have a VERY stable tank) will keep the DSB
stirred and prevent the formation of dead spots. Dead spots will create hydrogen sulfide which you don't want. The lower areas of the DSB
should be anoxic, but not anaerobic.