I've been using Jurassi Cal (from the reptile section) which is pure calcium carbonate and nothing else, but it clouds the water and I've been concerned about that and how much to use because it says to "sprinkle on food". But if you say that is ok then I won't worry about the clouding anymore. I also use Kent's Marine liquid calcium but I have no idea how much of anything to use.
I have been doing much the same, and coating microwafers in the powder and adding to the tank. But if theres an easier way to dose im up for it lol.