Scale-like buildup only in one spot.

[JamesR]

The pool has a raised beam in the deep end with a sheer descent. Seen in the pictures below. We continually get this thick crusty white buildup right below it at the water line. It’s been like this for the past 20 years. I scrape it off and it returns. Pool originally had an inline tablet feeder and I thought it was due to the concentration of the tablets flowing over that area. A few years ago I switched to SWCG. Still have the same issue. 10 years ago, we had the pool redone. New tiles and new plaster. Same issue before and after the renovation. What is it and how do I prevent it?
I chiseled some of it off just now and you can see it in the skimmer net.

 

[Rancho Cost-a-Lotta]

Every time your sheer descents run, they drip and splash water in the same spot. That water dries leaving behind calcium. This continuous cycle, daily, leads to a buildup of calcium. The buildup of calcium captures more water which aggravates the problem. You can test this theory by running your sheer descents for a while and turning them off. See if the water runs down to the calcified areas.

I'm not sure there's much you can do other than leaving the sheer descent off trying to remove the build up as it occurs.

 

[ajw22]

That is Efflorescence - Further Reading

 

[JamesR]

We purposely did not use the sheer descent since the last time I cleaned it, yet the stuff reappeared.

 

[Rancho Cost-a-Lotta]

Allen nailed it.

 

[ajw22]

Water is coming into the gunite through the back wall and migrating out through the grout lines taking minerals with it that form the efflorescence.

 

[JamesR]

Well that stinks. According to the article muriatic acid should dissolve it. You’d think the raised beam section of the pool would be less susceptible to backside ground water pressure. The raised beam is roughly 15 feet wide there. Yet the issue is only directly beneath the sheer decent. Its clean to the left and right if it. I wonder if caulking that open small area right below the concrete deck and above the sheer descent opening would help? There is a tiny slit there. Maybe when it rains, the water channels into that opening from the decking above.