Sand, Bacteria, Gravel.

JDM

Actually, AD wasn't comparing the efficacy of filter vs sand, he was relegating the substrate surface area to the role of just one more factor as "... in any tank the size of a beneficial bacteria colony will be relative to the amount of nitrogenous waste and the degree to which the tank is planted and/or has floating plants. So substrate surface area becomes nearly a moot point, especially when we also factor in the filter(s). "

And I agree, the substrate does become moot in a heavily planted tank when feeding is optimized... and I would take it one step farther and suggest that the filter is just there to remove the particulate matter. I only even did the sand vs gravel as a little mental exercise and thought some might be interested in the resulting numbers.

This doesn't put the bacteria completely in the back seat, as some bacteria do appear and grow and become just another stabilizing factor in a well balanced tank and they probably do so fastest in the filter.

I mentally took this farther, as there is more math that can shed further light on the filter vs substrate query, I just didn't think anyone REALLY wanted to read about the total volumetric surface area of a sponge too... then there is the matter of the ceramics in the "bio-media" and the silly "bio-balls".

Jeff.

AbbeysDad

I was not really comparing the BB colony in filter media vs. substrate. My point was more that the total numbers of beneficial bacteria in a tank is relative to available food, oxygen and other competitors. So the amount of sand or gravel is insignificant since the bacteria population has likely maxed out with even a thin layer of any substrate.
Now if we were to compare, filters do offer the unique ability to constantly deliver 'food' to the colony residents of the filter media...perhaps only compromised by the speed at which the water flows through most filters. With sufficient circulation, this might also be said of the substrate, but only in the uppermost layers.
I think equally important in the filter is the complex eco-system that develops with all sorts of bacteria breaking down and processing waste. This also happens on/in the substrate but at a much slower pace - still, substrate mulm can be very beneficial.
Finally, we should explore deep sand beds with the associated plant roots and critters. Deep sand was first introduced in SW tanks where they seemed to have distinct advantages. There are those that feel deep sand beds work equally well in FW tanks as well. However, it should be noted that to be fairly evaluated, deep sand requires a heavily planted tank, mts, worms and sufficient mulm to drive the DSB engine.
I have read a lot about deep sand, but have not tried it with all of the related components necessary.

AD

JDM

I'm halfway through a filter vs substrate comparison... it's more complicated than I thought at first but I'll post it when done.

The issue with the deep sand is it is not self supporting on the small scale that we employ. The worms and critters need a much larger area to properly diversify so there needs to be monitoring and replacing and feeding of the deeper stuff which, to me, is far more work than it is worth given that the real primary goal of aquariums in the first place is to be able to see some nice underwater environment that we would not see otherwise. Those that want to get deep into the whole self sufficient ecosystem are few and far between and everyone else who thinks it a great idea would give up very quickly... as it is I am sure the drop out rate for just a straight up aquarium is fairly high.

Jeff.