Hi All,
Very respectfully, there is a lot of very valuable information discussed in this thread, but there is also mis-information, even if offered with the best of intentions. Yes, I stopped responding after a rebuttal (post #26) to my post (#25) in this thread. Life went on with other things demanding more of my attention. I will try to be as succinct as I can in my response below and I will not be argumentative, just try to state my points, which I believe are well founded...
Below a brief review of what I said about how I run my canisters, which are in each case one of 3 separate large filters in each of my 6-foot tanks. I will also add a couple of things I omitted before:
1) I run pre-filters in all filters, which are cleaned weekly; 2) the 2 large HOB's in each tank are serviced fully every week (pre-filters and all media); 3) the canisters' media is serviced 4 times per year, sometimes more, up to 6 times; 4) I do regular water changes (over 70% weekly); 5) I turn all filters off during feeding, every time I feed. 6) I do not overfeed (intently try not to), and feed only 4 days per week; 7) My tanks are fairly heavily planted.
Using the methods above, virtually no food and also virtually no poop (or very little) goes into filters (any of either remains on top of the sand substratum in the tank, to be vacuumed weekly).
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"With all due respect, I think you may have misunderstood the meaning of canisters being NO3 factories."
I don't believe that is so. If little to no food or poop goes into filters, there is minimal accumulation of either in filters, and in any case, that is not the main source of ammonia and thus of nitrate.
Perhaps the main issue has to do with the means of Nitrogenous excretion in fish. With the exception of some fish, namely elasmobranchs (yes, including rays), coelacanths (nobody keeps any) and very few other teleosts, THE GREAT MAJORITY (UP TO OVER 90%) OF AMMONIA EXCRETED BY FISH OCCURS AT THE GILLS. Not from the digestive system (or liver, or kidneys), so not much contained in fish poop. In fact, FISH POOP IS NOT THE MAIN PROBLEM, in reference to ammonia and thus nitrate accumulation. Instead, the main source of nitrate is ammonia excreted by fish, which is dissolved in water (INVISIBLE LIQUID) is excreted by the gills. I am not saying fish poop is healthy, but it is not unhealthy for the reasons implied (main source of nitrate, which is not). That is why excess of it needs to be removed.
If one thinks of the aquarium as a system (comprised of the water, the tank, the substratum, the filter and media, and the fish and plants), dissolved nitrate (DISSOLVED IN THE FLUID MEDIUM) cannot be much more abundant in one part or another, unless that part is not exchanging much with the rest. One could say that anoxic under substratum places could be somewhat out of the that exchange, but that is another story, and not of relevance for the canister argument. A working and CLEAN canister which is pumping water in and out CANNOT contain water that has much more or less nitrate that the rest of the system. It could only if is is not taking water in and out all the time, or if indeed it is really dirty. But even if it is real dirty (not mines), nitrate is not a solid, and neither are its precursors, ammonia and nitrite. Also if everything is working properly and the canister is fairly clean, then the interior of the canister cannot become much different in terms of oxygen content that the rest of the system. Thus, it is not true that the canister by necessity creates anoxic conditions that may hamper the work of bacteria responsible of processing nitrogenous compounds in the system. So again, sorry but not.
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Regarding the last argument, related to the picture of clean versus dirty media in my canister (the picture I attached):
"Finally, with regards to the picture, the filters are still very dirty even if it's not solids (since as mentioned, a lot gets past the pre-filter). It's easy to see why, when compared to a clean sponge."... followed by pictures of BRAND NEW, UNUSED sponges.
This is now bordering on silliness. Any experienced aquarist (I am sure the poster included) knows well that sponges change color ('suffer discoloration') over time, from brand new to some months/years of use. If one squeezes further the clean sponges I showed, no further discoloration of water (i.e., release of particles, that is solids) can be observed no matter how much more one squeezes. Even if the sponge looks tan/light brown it is clean as far as nitrate matters: Nitrate is NOT A SOLID; it is dissolved in the water. If you test for nitrate in water where you have squeezed well (multiple times) a clean sponge, and compare that with clean water, there will not be much of a difference, or any. So comparing the color of a 4 year old but clean sponge with one that has never been used does not contribute to the notions being discussed in this thread.
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I want to end by saying that I don't post this because I want to win an argument or because I want to show that I am better (or worse) than anyone. I am not. I only do it because I see that some arguments offered are inconsistent with facts of aquatic life and it is important to have a better understanding of processes so we can apply them in our aquarium systems. People can take or leave it. I do the same. I have the highest respect for this site and all participants and would like to be be treated similarly. I am not implying that I feel I was treated discourteously because I don't, and I have fairly thick skin anyway. I did want to elaborate on my argument, and respectfully disagree with things I could not agree on. However, I don't want to continue (much) debating this issue, but I may look here and there for additional input and for kicks.
A useful lecture review of nitrogenous excretion by fish is in the link below. There are many other more academic publications (primary literature) looking in much further detail at particular aspects of nitrogenous excretion in fish, or for particular fish groups, but the review below does a good job of reviewing/synthesizing basic aspects which is what is most useful here.
http://www.yorku.ca/spk/fishbiol09/FB09lecture11.pdf (I believe one needs to copy/paste the link).
A final note similar to what I originally said: IMHO HOB's, canisters, sumps, sponge filters are not intrinsically better or worse than each other. Each one has its place, advantages, disadvantages, capabilities and limitations. And then, there is what you do with it, what kind of aquarium one runs and everything else. Apples to grapes, to oranges, to blueberries and everything beyond and in between.
