Total Pet had a large tank (180gal maybe?) in their store for a few months that had a black plastic bottom trim and sat on an uneven metal stand. The first time they filled it the bottom cracked immediately. In some cases putting a layer of rigged Styrofoam underneath is necessary. The rest of the time its just a good precaution. 
		
	
		
		
		
		
			
		
		
		
		
	
		
		
	
	
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