I have always done the same as Dan said. Custom built frameless with flat glass bottom, I use foam.  
 
  Black framed standard store aquarium like Oceanic, All Glass, etc. No foam. In fact I remember a thread on Rc where it was said that foam under one of those models would void warranty. As I said I read it, so take it fwiw. I have not used foam under my framed models, the largest being a 90g only.  
 
  My largest tank was a standard 225g 5/8th glass framless, under which I had foam. 
		
	
		
		
		
		
			
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				Doug
			 
		
		
		
		
	
		
		
	
	
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