I'm told muriatic acid mixed in water will lower the pH of my soil. Does anybody know how much muriatic acid to mix in a 5 gallon bucket? Will this work if I pour it around the base of a deodar cedar evergreen? My soil is sandy with a pH around 8.

Usually you would use sulphur or a product called miracid or Hollytone that is sold in bags, used by people who are trying to grow azaleas or rhododendrons. You want a dry product you mix with the soil to break down slowly, a water soluble one would wash away more quickly.