how deep does a dsb have to be?

i was thinking of a 4 or 5 inch sand bed in my 75 gal and about the same in the fuge is there any drawbacks for it being this deep?

 

Three inches or above is the definition of a DSB.

 

There's no need for more than about 2-3" of sand in your tank. Skimmer technology has come such a long way now the DSB is not needed to break down waste.
DSB tanks don't do well in the long run, they're like an IED waiting to go off and wipe out your tank once filled with toxic waste.

 

sweet thx guys i ll stick with the 3 inch bed in DT and fuge