Originally Posted by Hallyx
Indeed it is an informative thread.
AbbysDad's comment about the efficacy of sand vs. filter media in harboring nitrifying bacteria, reminds me to ask a question which has intrigued me ever since I cycled my first bare-bottom tank.
Is a few cubic inches of dense filter media, even though it contains a smaller colony, relatively more efficient than a much larger amount of sand? At what relative sizes would they be equally efficient?
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.