I'm seeing this white stuff pushing out of (and sometimes actually pushing out) the grout in the tiles that separate my spa from the pool. I don't see this happening anywhere else in the pool. It's very hard and not easy to scrape, suggesting it's not salt.
Any ideas what to do? What about the areas where the grout is pushed out? What kind of grout can I use?
In case it's needed, latest chemistry:
pH 8 (usual value)
Salt for SWG 2900 (came down with recent rain from about 3400)
Calcium hardness: 400
Cyanuric acid: 85