Sand bed thoughts

[Diomedes]

Sinks? Sources...

The DSB is both a Source and a Sink. These are opposite terms used to denote things that either provide something or take something away. In nature the Mangrove swamps and Seagrass Flats act as a Sink for some of the nutrients produced by the highly productive reef, which is a nutrient Source. A properly set up aragonite DSB is a Source of natural minerals and buffers (Ca, Sr etc.), can be a Source of natural planktonic and larval prey items for filter feeders and corals. If there is a ton of rotting material in your DSB then it is a Source of phosphates and other nutrients that are released by fungi and bacteria. It is a Sink for Nitrate, meaning it absorbs Nitrates. I think a properly set up DSB is better than Live Rock at Denitrifying, but that doesn't mean it has to be in your display, under your lights, accumulating detritus. It can be a separate filtration component altogether, plumbed in line.
As far as DSB's accumulating toxins...Do you mean H2S or Heavy metals?
Aragonite is constantly dissolving so that would release the bonded heavy metals back into the water. H2S is not something I have experience with...It used to be a big concern when LR wasn't being used along with the meiofauna it imports.

Stephen