Nice, very nice.  As for gravel cleaning, maybe some kind of a plate that it sits.  Then make the plate aggitate some and then some kind of a force of either air or water jets on the bottom to push the debri from one side of the tank to the other.  Sort of like the way a river pushes debri and sediment from the river top to the river bottom, just have it drain out a screened tube into a drain.  Now that would be cool to incorporate that.  I know, my imagination is out there.  But that would be cool as heck to see.
				
			
	
	