I have kept a 120 gallon experimental reef system for two years now, which is plumbed into a 450 gallon seven tank system to experiment with filter feeding organisms. The bottom contains 4-6 inches of rubble which was supplied to me by CaribSea (thank you, Rick Greenfield!). I worked with this material for a number of years in different capacities. The pieces are typically 25 cent in diameter. They sit on the bottom.
Before the present tank, I did one with these pieces and Caulerpa. That tank didn't do well; the Caulerpa grew between the pieces so densely that it trapped too much gunk. I didn't like it.
The present bare bottom with 4-6inch rubble tank has matured, and contains a huge amount of life- small brittle stars, pods, worms, including tube worms, and a heavy sponge growth. Surprisingly, there is at most 1/4 inch of very well worked detritus on the bottom- and this is a very heavily fed tank (twice to three times daily feedings for dendros by target feeding of copepods, oyster eggs, phyto, golden pearls, many other things over the years- sometimes feeding at much higher rates).
There has been NO significant accumulation of detritus.
I believe that burrowing animals eject material that is carried out of the aquarium into the skimmer. The fine stuff on the bottom is probably live rock borings.
I also have an Eco-Wheel algae scrubber on another tank in the series, that has a bare bottom in it- that too has at most 1/4 inch of detritus, very well worked.
I am quite sure that detritus will not be a problem over the long term in a rubble tank- whereas I am concerned about detritus in a sand bed (Vibrio and basically going sour in there, especially with tanks that are heavily fed). I have set up many, many tanks over the years basically experimenting with substrates.
I recommend the rubble substrate; it's also a good way to start frags.
Charles Matthews M.D.
