I have that sludge too...and surprisingly it doesn't go past a certain depth.  I'm thinking it may just be "eaten" by the enzymes to a certain degree.  I had the same thing in the bottom bucket in the 12 wks I had the meaties and it was the same depth...no more, no less.  You'd think it would grow and grow until the bottom bucket would be all sludge but it doesn't.
	
		
			
		
		
	
				
			
	