DSB vs Bio Balls
From Marine Aquariums of South Africa - wiki
Most LFS stores will suggest that Bio Balls are the way to go however there is a big difference in the final stage of how they break down waste.
The big difference between bio balls and a DSB is the end result, bio balls are excellent at biological filtration and are super efficient at converting ammonia to nitrite and then to nitrate and that is where the filtration stops. Although a low amount of nitrates are not harmful to coral or fish, algae goes mad for it so high nitrates=algae. The DSB has a further step because of the anaerobic conditions deeper in the sand and converts nitrates back to nitrogen gas i.e. complete nitrogen cycle.
Bio Balls also trap detritus meaning they need to be cleaned/vacuumed on a more regular basis.
