Upside down sand beds

[BCOrchidGuy]

Rikko apparently it doesn't defeat the purpose it just alters the process and supposedly makes it more efficient. The Plenum isn't an anoxic region anymore it's more a region to let water slowly creep through coarse aragonite and then up through fine aragonite. Theoretically it triples the effectiveness of the sand bed. There should be a slight film on the bottom of the sump (on the glass) and that film works as a surface as well.
The design allows slight upward pressure and also increased water movement through the sand grains. You end up with two surfaces that are not illuminated so you get no algae growth plus the conventional top surface. Three surfaces, cool huh? You have the floor and the upside down sand bed and the typical DSB surface. The article recommends the use of photosynthetic organisms on the upper surface.

Doug