If LR rubble has more surface area for nitrification.....
then great, that is an awesome reason to be using it. If you have nitrate readings in your tank, that is because you have too much pollution in your tank... not because you have too much LR or LR rubble in your tank. To control nitrates, you can use nutrient export (eg, macro algae growth, water changes), or you can employ different strategies to encourage anaerobic denitrification (dsb, coil, large LR), or you can reduce the waste that is introduced into the system (lighter stocking levels & feedings), or do a better job of removing it before it begins to break down (better skimming etc). However, removing LR or LR rubble from your tank will not improve your water quality... it will hurt it bad. This is because the nitrifying bacteria are helping you... it's not their fault that you are getting the readings you are getting... the problem is whatever's going on in the system that is providing them with so much food. Reducing the amount of beneficial bacteria will not do anything to address the cause of that problem. You can't improve your water by trying to limit the amount of nitrifying bacteria...
I have actually learned a lot from this discussion - especially about the denitrification capabilities of LR. After hearing about why larger rocks are essential for denitrification, I am a little discouraged to say that I don't think it is very helpful to us with nanos. For example. choose the largest rock in your tank - now picture that every part of the rock that is exposed to oxygen rich water is colonized by nitrifying bacteria to a depth of 2-3" (as has been explained). If you were to shave off 2-3" of every part of that rock that was exposed to oxygenated water - bearing in mind all the indentations and holes and tunnels through it - how much of that rock would be left? Anything? A sliver? That is the denitrifying region of your rock. Now look at all the nitrifying region that your have shaved off. In a nano tank, I would really be surprised if any of our aquascaping rocks have those denitrifiying regions - regardless of whether they are solid pieces or broken up rubble.
If you really had you heart set on denitrification via LR, then I would respectfully submit that you can still fit a much larger piece of rock in a canister than you could in a HOB filter (in fact, I could have fit a much larger pice of rock in my canister filter than I could have in my whole tank). Realistically though, I think we are stuck to taking the approach of limiting the amount of nutrients introduced into the system and of controlling our nitrates via nutrient export - like our good old water changes.
just dave,
I have to say that that is an amazing collection of nanos, I would love to have a set like that! First class job on all of them - you should be proud.
And great point about the problem being with canister filter users/practices and not with the filter (wish I had thought of something as succinct as that without rambling on
)
Edit: and so does everyone else...
_ Chad
.
What would really be interesting is a plot of your nitrate levels over time, with a marker for when water changes occur. 
