My advice is to return them if the store will accept them in return. 
 
IMO a reputable store wouldn't sell them to you (or would strongly advise you not to get them) if you have a 75 gallon tank. 
 
A few issues that will come up include physical room for swimming, waste production (a large metabolically active fish producing a lot of waste) and the potential for aggression in a small tank, even though these are said to be among the less aggressive triggers. 
 
I don't know the actual recommended size for this species of trigger so someone who has personal experience with this fish might want to chime in. 
		
	
		
		
		
		
			
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				120 gallon sps/anemones/LPS reef since 2004 
Apex controller 
8 x 54 watt T5 PowerModule 
Herbie's silent overflow system 
Jebao DC 12000 return pump 
Jecod CP-40 Cross-flow circulation device 
Mini Bubble King 180 
Barr Aquatics calcium reactor 
Bucket fuge
			 
		
		
		
		
	
		
		
	
	
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