A naso or powder blue tang will get rid of it i know my new powder blue tang i got loves algae hes always cleaning my rocks same with my coral beauty. IMO emerald crabs dont do much mine hasnt + i never see him. 
		
	
		
		
		
		
			
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				90G AGA Reef Tank + 30G Sump 
90G AGA Seahorse/Pipefish Tank + 20g Sump
			 
		
		
		
		
	
		
		
	
	
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