Sorry about the hun thing, lol ..bad habit.
See Nikki this was the whole reason I started the plenum thread. The concept was to let everyone know how things work biologically, that way it gives you a better chance on manipulating it or know if what ever system can even work. Ok lets get to biz of breaking down a DSB.LOL
When looking at a system like this we have to look at limiting factors. knowing these can help us fool around.
When worrying about a bed going anaerobic, we can look at these limiting factors. the presence of oxygenated water will not allow it to go anaerobic, so we know then that we have to do that. Now because the grain size is so fine its harder (you can kinda see where I was going with particle size in the plenum) but not impossible. large stiring critters like cukes, or big stars stuff like that. Or a million worms and a billion pods. you could introduce more sand no problem, but I dont think it would make a big enough impact and as time goes by you wold have a sand tank, lol.
Even knowing the problems with a DSB I did one for 2 1/2 years, figuring I could out smart it and manipulate it to where I could make it work. Manualy stirring the bed and syphoning out the detritus that came out of it worked for me in keeping that upper level aerobic. With the rocks on top of part of the sand I couldnt do anything their but hope the bugs could manipulate. I spent hundreds of dollars of detrovoir kits and so on. The sand under the rock was anaerobic and had a sulphide zone 1/4 inch down. In the display I was able to keep the anaerobic zone down about an inch. Sulphide zone down about 1 1/2inches. I battled the phosphates (and believe me I know a few tricks) but couldnt win, the battle became more and more of a loss (as in cyano/algae blooms) were coming back more often and quicker. Their is no way a DSB cn deal with phosphates, you only chance is to make sure you limit the ammount you put in.
Can I ask you a question, why is it that you want one??
MIke