Adding Calcium Carbonate

I occasionaly add calcium carbonate to my aquarium to help harden up the
water. I crush up tablets and mix them with tank water to make a white
suspension, let it sit, shake it up well and add it to the water. It clouds
the water for a little while before it settles or disolves. I've been
wondering -- would this be hard on my fish? Would these suspended particles
be hard on their gills? And if it is what would be a better way to add the