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			#1  
			
			
			
			
			
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|   Yup, I've repaired cracks below the waterline successfully like this. 
				__________________ Dan Pesonen Umm, a tank or 5 | 
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			#2  
			
			
			
			
			
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|   if you can, silicone another piece of glass from the inside of the tank using silicone.  Make sure you put a nice bead around the edge of the glass to give it a good seal. |