You can pick up a very pure grade of sodium hydroxide at a great price from Voyageur Soap and Candle in Surrey. 
 
Be careful with this stuff as it is very caustic, not sure if I want to run it through my doser.   
 
I have used this sodium hydroxide mixed with kalkwasser to spot treat undesirables in my reef tank. 
		
	
		
		
		
		
		
	
		
		
	
	
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