Keep temperature swings low, if increasing or decreasing temperatures do no more than +/- 2 degrees a day. The more stable the environment the fish is in the more functional its own immune system will be. I usually like 75 as the min and 78 as max gives a little wiggle room both directions if something goes awry. Ei the fan in my sump went last night and my tank is reading 81.3. If i had the set point higher this might have pushed me into a dangerous area. Instead i just put a cloud function on my lighting app till a new fan arrives.
73 is ok but say your house temp drops tonight and your heater fails off, your tank is now 65 degrees.