Hi all,
I am pretty sure that most of the beneficial bacteria live in the filter media, so I'm not conviced that there is enough bacteria in the gravel or on the plants to make much difference.
It depends a bit on the set-up, but my suspicion would be that in a planted tank, with a substrate, a lot of the nitrification occurs in the upper layers of the substrate and in the root rhizosphere.
I also think it will be different for every-tank, dependent upon the substrate, the filter media and the degree of oxygenation. In some ways it is just a numbers game, you are going to have a larger oxygenated volume of substrate and surfaces.
I stripped the tank down that has been set up in my <"
kitchen for the last 10 years">. The substrate was 80% fine play-sand, and it has always been fairly heavily planted, substrate depth varied, but was always at least 4 cm (and often deeper). It has always had MTS snails present. There was a layer of fine roots at surface level, running through a mulm layer, and the large
Echinodorus had rooted across the whole tank, but I expected that there would be layers where there was evidence of anoxic or anaerobic conditions, but there weren't any discoloured layers, and no smell of decay of any kind.
cheers Darrel