Is it safe to swim in a pool with high calcium hardness?

Yes, it’s safe. Calcium hardness is just dissolved minerals, not a toxic chemical. The main issues are cloudy water, scale on tiles, and clogged filters, not health risks. Your eyes might feel dry if levels are extremely high (800+ ppm), but that’s usually due to pH and alkalinity being off. Don’t cancel swim practice, but test and balance the water if the pool looks dingy or has white buildup.