Originally Posted by AbbeysDad
Says you - slowing down the flow rate of highly oxygenzted water doesn't remove O2...( My head is starting to hurt
Sorry for your headache, but more biology lesson (sorry). PhD. in wildlife and fisheries science, 20+ years teaching at universities, my wife teaches microbiology and manages the microbiology lab. I'm pretty confident in the info below. No charge for this lecture
. Sorry it's so long, I don't know how to explain it otherwise...
As I mentioned earlier, there are some bacteria that are facultative anaerobes. That means they work either in the presence, or in the absence, of oxygen. No matter what anyone here says, I bet I can culture multiple bacterial species from any FW tank. The idea that only one or two species of bacteria inhabit a tank is just not biologically accurate. I'll bet $$ I could isolate some anaerobes or facultative anaerobes. A key point to remember is that bacteria (except strict anaerobes) consume oxygen just like the fish do.
To the specific point you raised - the more bacteria grow, the more O2 they consume in the filter. As the water flow slows through the filter, the bacteria in the filter have more time to remove O2 from the water via their aerobic respiration pathway. The water, in effect, is bringing through less O2 volume/minute. Same as adding more fish to a tank=more O2 demand. Once the O2 level decreases past a certain point, the facultative anaerobic bacteria have the ability to change their cellular respiratory pathway, the net effect is then they can use the nitrate.
This also explains why water exiting the filter is O2-poor. The bacteria in the filter have consumed the oxygen from the water. It also explains the periodic feeding "boost" that's required to keep the bacterial population high enough to generate anaerobic conditions. The typical canister, as you said, works with aerobic bacteria and requires oxygen. Aerobic bacteria typically metabolize faster, but can't reduce nitrate.
The one thing I really can't figure out is how the Matrix stuff it would work in a wet/dry filter (drip tray) and any canister filter as claimed. The wet/dry certainly isn't typically ever aerobic!
Shoot, thought I had it figured out, now my head hurts...