Sentence 1: Nick needed to clean his turtle's tank. 
 Sentence 3: Nick scrubbed the sides of the tank 
 Sentence 4:  He proceeded to fill it with fresh water 
 Sentence 5:  The tank looked crystal clear when he was finished 
 Option 1: He used a gravel vacuum to remove the old water. 
 Option 2: He used a fish tank service.