sealant that will protect stone in chlorine pool

 I am trying to educate myself on ways to clean and hopefully seal (if not possible, at least slow down) the efflorescence at the waterline of our pool.  The coping and waterline tile is sandstone and within 2 years has developed a distinct and unsightly white line.  The advise I have received so far is if power washing with acid doesn't do the trick (and it hasn't) that glass bead pressure blasting in the only thing that will remove it.  Is there any sealant that will protect the stone in a chlorine pool?

I'd appreciate any help I can get!!

Thank You.