I know Muriatic is Hydrochloric acid.  I use it for eating aluminum and removing the Galvanized coatings of of metals.  It will leave a residue and most likely render the tank useless. 
 
Why not just a really diluted vinegar?  I would think 5-10g in freshwater would loosen up the coraline after a few days 
		
	
		
		
		
		
			
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				Dan Pesonen 
 
 
Umm,  a tank or 5
			 
		
		
		
		
	
		
		
	
	
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