Yes, you should test the Calcium level to determine if you need to change water or dose Calcium. Alkalinity is even more important so don't forget that test either.
Any Calcium chloride supplement will work just fine to increase Calcium, there are plenty on the market. More is not better so don't overdose. I use limewater to maintain both Calcium and Alkalinity. When I need to only increase Calcium I use pure Calcium chloride. To raise Alkalinity only I use baking soda.