To dose something or not, is driven by the tank needs as everyone else has said. What your tank needs is driven by what you stock, how often you do water changes, and the like. If you're doing 10-15% water changes weekly, then you may not need to dose anything. If you have a large amount of corals consuming a lot of mg, ca, alk, daily, then you should probably be dripping something.
Generally you don't want to just be throwing in a gallon of kalk at once. That could throw your PH off, and could make for some unhappy inhabitants with the sudden influx of ca and alk as well.
This probably would get more response from the chemistry guys in the reef chemistry section. Chemistry is what coral care really is all about.
And my 125g goes through a 5 gallon bucket of kalk water (with ATO) in approximately 3.5 days. Which is a little over a gallon a day! Half a gallon is nothing.... It's a lot for someone manually doing it, but, I have to fill a 5 gallon pale every 2 -3 days! (I don't like it getting too low...)