and plenums are very different to each other. A DSB
is very fine sand set in the tank from depths of 1 inch to whatever you want. It is a system slewed for the population of bacteria and acts as a recycling center with no export beyond nitrogen (according to the experts, toonan, dr. ron, S. gamble).
A plenums main problem in the hobby is that most folks dont set them up right. A plenum is supposed to have grains that are the equivilant to 4 to 5 times the size of CC
. With a plenum being completely set back off the glass to not allow the penetration of light.
The biggist difference in the 2 systems is that in a plenum with the coarsness of the grain and good water flow will keep the substraight areobic and thus well oxygenated. This allows for good nitrification. Below the plenum is the are of anaerobic. This area id devoid of oxygen and is where denitrification occurs, also due to its low PH
you will get good remineralisation. (bufferin compacity).
With the DSB
its tiny grain size allows for greater surface area and thus more bacterial population. Also because of this size grain the anaerobic zone is much closer to the surface (1/2 inch down according to Rob Toonan). This makes for a smaller nitrification zone and a larger denitrification zone.
Both systems have thier pros and cons, but are still recyclers (they create bacterial biochemical cycles) and do not export beyond nitrogen based waste.
The plenum I would have to say is a high energy system (mainly because its grain size makes it less likely to get suspended) and a DSB
is a lower energy system (closer to that of a lagoon/swamp and so on.
Logan a way to measure o2
is easy for any system (dsb
/plenum) you can simply look at the side you the bed and look for the line. Thiser will be a defined line in the sand layers (sometimes it is darker in appearence or black). this line is the change in zone between areobic and anaerobic, or oxygenated and non oxygenated.
To add a third opinion into the mix there is no way to call any depth "optimal" because it will vary greatly depending on different factors in the tank including waterflow, etc. One tank could effectively get the anaerobic zone with 3" of sand while another tank may require much more.
Agreed totally. An anaerobic zone can occur on the surface even (inside a lump of detritus). A DSB
is not a static thing it is in a constant state of flux. With bacterial and algal population increasing and decressing as the food source goes up or down. Acording to Rob Toonan he feels that the anaerobic zone on most hobist tanks occurs around a 1/2 inch down.