Many of the planted tanks I have seen use wood but I have always used rocks. Never had any trouble with the cables. Always laid the cables covering the entire bottom of the tank just in case I wanted to re-do the landscape at some later point. Easy to move rocks, the Dupla cables are a take down the tank item to do it right - uses little suction cups with a plastic piece across the top to hold one run of the cable on each side (kind of like a telephone pole that only holds one cable on each side).
I would bet that whatever accumulates under the LR would be coming from the sides or the LR. If there were cables underneath the LR, there would be a pretty good convection current coming up around the edges taking that stuff up too.
I have never put anywhere near as much rock weight on the cables as you reefers use so I wonder about the cables in this application. Maybe if you set up an egg crate shelf across the bottom of the tank (or at least under the LR) with cables underneath you could do pretty much what you wanted with LR on top.
Also, I will add that I have done something a little different with the heating cables than most. Dupla was undergoing some changes (the original guys sold out then the new guys sold, and I think maybe they sold too). About the time of the last sale I noticed in their literature something about keeping the cables on longer with even lower wattage heating tahn they had previously recommended. So I got a small Peltier effect chiller and forced the tank temp down to the heater temp setting. I do not have it set to bring the heater on all the time but it definitely comes on far more frequently and for longer than it otherwise would. I know of others that use higher wattage cables and have claimed good results. I am not sure that either way is better, or if either really works.
I think a lot of the idea is to provide a slow moving current that gives the polluted water time to do the reduction thing in the substrate (isn't that what is going on down there in a DSB?). Then be heated and moved up into the water column so that the normal filter can take care of it. In this way there is no accumulation. However, they are also using live plants. Some of this stuff is taken up in the roots, perhaps by the leaves too from the water column. Remember the principle of a refugium.
Look, I stated initially that I have no idea about this - I just know enough to be kind of dangerous.
I am not recommending this as a solution. I am only kind of regurgitating some info from my FW days that appeared might be a solution to this DSB problem. I was pretty good in Chemistry but that was atomic level stuff and this is more biology to me. I just brought it up to see if any of you expert bio guys had any idea about it. Maybe I should start a thread on this??
I will add that Dupla recommended a specific size range of gravel for this to work - 2-3 mm (or maybe 2-4). SOme of this size selection was to permit root growth. Too small and it would not let roots grow well, too large and the roots did not have enough to hang on to. I'll check if anyone wants to try.
salty joe,
Fluids and solids are pretty incompressible - least as far as I know (I'm an EE), or least no where to the extent gases are. But all substances change density with temperature to some degree. It gets colder, higher density. It gets warmer, less density. However, water exhibits a temperature dependent characteristic that no other known substance does. Right around the temperature at which it changes phase from liquid to solid its density increases slightly over a degree or two range, then it goes back to the slope (graphically speaking) it normally follows. This is what makes ice float. It is also what keeps the oceans from freezing over thus making the planet a large ice cube. IOW, it is why there is life as we know it on the planet. Amazing how such little things can make such a big difference.
Thanks
Charles
