Kalk paste might work, (google techniques, dangers, etc). Or else you may just have to grind at it a little every day until it finally gives up. Mucking gloves from Lee Valley will make it a little less tiresome reaching into the tank. 
		
	
		
		
		
		
		
		
						  
				
				Last edited by soapy; 01-26-2016 at 01:07 AM.
				
				
			
		
		
	
		
		
	
	
	 |