We have a two year-old 26,000 gallon salt water pool with Jandy equipment and "pacific blue" plaster. Last summer, we started seeing little hard white spots scattered around the bottom, interspersed with just a few larger ones. The bigger ones look kind of like bird droppings, the little ones are just sharp points. Here's a photo I took today of an 18" deep shelf (sorry about the reflections).
Our pool service company says this isn't typical scale -- they aren't sure what these are, although they believe it may be calcium coming out of the plaster. We've never had any scale or deposits at the water line, although our water is a bit hard (400ppm) and they've suggested draining 1/2 the pool before it gets warm enough to swim in to reduce that). The spots are mostly on horizontal surfaces and can be scraped off with a credit card but that would get a bit tedious for the entire pool.
We did have some problems controlling the ph last summer (when the water was warm enough to swim in), and had to add acid twice a week. The ph would range between 7.8 and 8.5. We also had to treat the water for phosphates -- got up to 1,000 ppb but now it's down to 200ppb. We have a lot of trees and the pool is kind of a mess in the fall (elms) and spring (live oaks), but we can deal with that. The little spots are the only problem -- never had algae problems at all, and the water is crystal clear. The other chemical levels are ok.
Any ideas or suggestions for additional tests would be welcome.