No, as was said, sand will not work for long at all@Paul B can an RUGF be effectively used with a moderately deep 2-3" sugar sand bed? I already got the sand with wrasses and gobies in mind.
Mud will accumulate in anything after 30 years. If you stood still for 30 years, mud would accumulate under you.I guess one reason I'm questioning this is because Paul has a picture of his plates being lifted up out of the tank covered in "mud".
Remember if you have an established reef and not one that people take down every 15 minutes to catch fish to put in quarantine, the corals and rock will be kind of cemented together so it is very hard to move and you can't physically get under there to stir it up.
That mud in my old tank was mostly under the rock. I think I lifted the UG filter plates then to re aquascape because I built a lot of new, large hollow rock out of cement and I gradually came up with the theory that a reef should be a lace like structure so water can flow everywhere and now my tank is like that.
The tunnels go from one end of my 6' tank to the other. It is entirely caves and holes which is why I can have fish in there for a year and never see them.
WE may not like that but the fish love it. This is a huge problem in all these tanks with disease. Most people can't read the expression on a fishes face and fish in non natural looking tanks have an expression like Nancy Pelosi. Think deer in headlights. ;Wideyed
Fish that feel safe and are fed correctly never get sick.
It's like if we were abducted by Aliens (from space not South America) and they were really ugly looking beings and they kept us in a place that was built out of old Milli Vanilli CDs (Google them)