It is possible that the blue sand in your Polaris vac is actually small pieces of your pool's plaster. Over time, plaster can wear down and chip away, causing small flakes to enter the pool's circulation system. This can then be picked up by pool cleaning equipment such as your Polaris vac.

If your pool's plaster is indeed showing signs of wear and tear, it is important to address the issue before it becomes a bigger problem. Not only can chipping plaster cause unsightly discolorations in your pool, but it can also lead to bigger issues such as leaks.

If you are experiencing back pain and suspect that the pool plaster may be exacerbating the issue, it is important to seek medical attention before continuing to swim. Plaster particles in the water could potentially irritate and worsen any pre-existing back conditions.

To prevent further chipping and deterioration of the plaster, consider hiring a professional pool maintenance company to evaluate and repair any damage. In the meantime, regularly inspect your Polaris vac's filter for any signs of blue particles and replace as needed.

Remember to always practice proper pool maintenance to ensure a safe and enjoyable swimming experience for you and your guests.