There are no cal - hypo tablets for the residential market. They do make them for the commercial market with special feeders. But they dissolve very quickly.
Updated****
I stand corrected. Their are Cal Hypo tablets marketed under NST Chlorine.
Check that out - I am so I can reference it in the future.
I hate to use the dirty "S" word but Sustain tablets are 3" Calhypo tablets. They are inserted in a plastic container that has an adjustable hole in the lid to adjust the rate of chlorine used and yes they do melt fast. This container is placed in the skimmer. If I recall correctly they contain only calcium hypochlorite. I have sent an email to the manufacturer to confirm this. I've been using these and it works for me.
Mike.