Algaecal has a calcium without Strontium included. The calcium is made from algae. And my doctor recommends calcium from plant sources as they are absorbed better.
The other thing to be aware of is spacing out calcium tablets. The body can only absorb so much at one time. Also be aware of foods that also reduce calcium absorption- nuts, spinach and any food with oxalates. If you like nuts and spinach, eat those at a time when you are not taking your calcium supplements.