I use an algae based calcium supplement, New Chapter Bone Strength. A daily serving of 3 pills has 905mg calcium, vitamins D3, K1, K2, magnesium and a trace of Stronium which occurs naturally in the algae. A 40 day supply on Amazon is $40. I've used it since I was diagnosed with osteoporosis 6 years ago and my DEXA scores have remained stable. I am due for another DEXA in a couple weeks.