My son, who lives in Dallas TX, is having a problem with erosion of the stones above the waterline tiles. The saltwater pool was existing when he purchased the home. He has tried a few attempts trying to stop this erosion but to no avail. He has tried a product called Porous Plus, carefully following directions, but it did not work. Is there another product that may be better, or easier to apply than the Porous Plus or is there a secret to the application process that he should try. Thanks in advance for any information you may have.