@loplady therapeutic dose of strontium is 680mg. Maybe you can find out if 5.5mg affects the DEXA.

I've read the strontium is a natural part of the algae. From WebMD: "Strontium is a mineral found in seawater and soil. In your diet, you get it mainly from seafood, but you can also get small amounts of it in whole milk, wheat bran, meat, poultry, and root vegetables. Strontium is similar to calcium. It seems to play a role in how your body makes new bone while it slows the breakdown of old bone. That means it may affect how strong your bones are. Some research says that women with osteoporosis may not absorb strontium as they should."

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.