72 is low for a reef tank, setting it higher should not effect your peak temperature very much. What I am saying is (for example) 80-84 is a better range then 72-83. Try setting your heaters a little higher and see if you can minimize the temperature swing.
My tank runs between 80-82. I found that when I was adjusting my heating system it did not matter how low they were set, the tank would still reach the same peak temperature.
Just my .02
