run low vs slacken

run low

verb
  • To near the end of a supply of something; to be nearly running out. 

slacken

verb
  • To gradually decrease in intensity or tautness; to become slack. 

  • To make slack, less taut, or less intense. 

  • To deprive of cohesion by combining chemically with water; to slake. 

How often have the words run low and slacken occurred in a corpus of books? (source: Google Ngram Viewer )