Many people mention Algaecal because it's plant based. A similar product is one I've taken for about six years: New Chapter Bone Strength calcium. Like Algaecal, it's plant based from algae, but it's much cheaper. You take 3 pills a day and a 40 day supply costs $39.88 on Amazon. Their site on Amazon says it's "USDA Organic plant-based calcium from sustainably harvested Red Marine Algae that’s rich in bone-nourishing calcium plus magnesium and 70 plus trace minerals". It has vitamins D3, K1, K2, and Magnesium. Like Algaeal, it has a trace amount of Strontium because that naturally occurs in algae. My DEXA scans for the past 6 years show my osteoporosis has remained stable.