What purpose do you want the DSB for? If it is solely for nitrate reduction, then there's a huge thread on this at RC. Just do a search for remote deep sand bed or (RDSB).
I have one of these on my system. Basically, it's a 70 liter trash can full of sand, kept in the dark, and has "clean" water flowing over it at a relatively high rate. I have no clue whether I am getting any benefit from this or not since I changed multiple factors with the tank at the same time. However, I did have enormous amounts of HA prior to its addition and I have almost none now. I was a bit desperate at the time and willing to try any form of snake oil.
If you want the DSB for critters, etc..., then please disregard.
Cheers,
Steve