Im not going to offer much advice on this one. 
But yah toss the sand else you gunna pay bigtime, keeping half is gunna be bad. 
If anything keep a few cups and place on top your new sand, a 1mm or 2mm of your old sand, preferably rinsed in same tank saltwater. 
 
I hear alot of clients who have had nothing but troubles on this topic of tank moves. 
 
Keeping a bit of the old sand helps seed the new sand, but keeping 1/3 or more of the old sand will cause an ammonia spike so bad u may loose in the end. 
Spend 50$ and save the life's of your corals and fishys. 
		
	
		
		
		
		
			
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