NaH2O said:
What is your understanding of a plenum?
As I understand it, the plenum was popularized by Dr. Jaubert in the late 80's early 90's. It's main idea is that an anoxic (extremely low oxygen, but not 0 oxygen) pocket of water under a sand bed will naturally remove nitrates from the system. The low O2 will also lower pH in the plenum and the low ph will thus break down the aragonite, releasing beneficial minerals into the system.
I used the same size grain for the sand bed over the plenum because I read somewhere that a finer top layer will cause anerobic areas, while a uniform size grain allows the nitrate to be turned back into its natural gaseous state. To be honest
, I followed the instructions for a plenum on Garf's site.
After thinking about yanking the plenum this weekend, I began to think that the size of the sand you use would make a big difference in determining flow over (or into and out of) the plenum. If the grains are too big, would this let low pH water or other nasty stuff out of the plenum?
Also, will the plenum ever get "full"? I mean, just so old or used that it won't stop denitrification?
I chose a plenum over DSB because, as I understand it, a DSB creates a anerobic area to break down nitrates. But it only breaks down nitrates into ammonium, and that's it. Isn't ammonium a nutrient that contributes to algae growth?
So now I'm worried about both, and I really want to try a bare bottom tank. I really only want a little sand for aesthetics. So what about my nitrates? I guess water change will be the only way?
