Is it only where it is raised?
How hard is your water?

Scott

Yes, only the raised section (although I get some calcium build up under the waterfalls) which comes off with a muratic acid/water srcubbing. I have not tried to clean the spa tiles (in picture) yet as I don't know what it is or what cleaner it will respond to.

The water hardness (Cal) is 180, Alk is 120, PH is 7.5, Cya is 30, water temp = 87F and salt is 3200ppm

Thanks for responding.

It will come off with a scrubbing and 4-1 water/MA mix but let the alk drop some, say to 80 or 90.

The pic shows it's been there some time. It will ease over time but expect it to continue at least a few more times while the excess calcium leaches out of the thin set and grout.

Scott

Does the spa spillover into the pool?
How high is the spa water?
What type of material was used between the bottom of the coping and the top of the inside waterline tile? Standard grout, waterproof grout or silicone?

I understand the excess calcium will eventually stop from the grout and the thin set, but I might try maintaining your calcium levels closer to 300 to avoid the water seeking out calcium. If it's 180 now, it could have been very low at the last fill. You could always test your fill line (or hose) water's hardness level to see how soft the initial fill was.