alk powder?
do you mean just mixing baking soda in your top off?
if so, you can do it that way if you can figure out the correct ratio of evaporation to your tanks needs. but it only adds one part. the alk. you would still need to dose Calcium daily.
Kalk delivers both CA and alk in a balanced proportion, but again, you need to know what your tank is using daily and how much it evaporates if you plan to add it in your top off.
I guess you could add premixed Kalk at the proper ratio daily but you would have to keep an eye on your ph as it has a direct affect on it dosing many times a day.