Bio beads are basically the same as vsv dosing, they are a carbon source and housing for aerobic (oxygen eating) bacteria, this bacteria does not eat nitrate. The bio beads are consumed slowly, as the bacteria reproduces and dies, NO3 and PO4 and O2 are used up in the process, but the bacteria has to die and be skimmed out to remove the NO3 and PO4 from your system. There is no way to control it.
Sulphur is also a carbon source feeding bacteria, the sulphur is consumed slowly (should last @ 2 years), but the bacteria is anerobic (nitrate eating) and lives in the reactor, it has a natural life cycle, and only live in a low oxygen enviroment. It is important to not build the reactor too big because when the nitrates are reduced to nil it may be necessary to remove some media to accomodate the reduced load. It can be controlled with an ORP controller.
I have read studies that show DSBs do not have the nitrate reduction capability beyond a light bio load,eg. a few fish and a few corals.
I have tried a DSB in the tank, in the gium, and in a bucket to no avail, my bio load is too great, (18 fish, many inverts and lots of corals). My nitrate problem began when my bio load got high.
The denitrator does not eliminate the need for water changes as at least a 10% monthly is recomended to ensure ionic balance, but some systems were run sucessfully for years without water changes.
Give me another week or two to see the results of the sulphur change.
BRS does not sell sulphur. Oceans Direct.ca does, search "sulphur"
