I looked at the photos in your other thread.
Due to the fact that your pool is only two months old, IMO, it is not a calcium scale problem, at least, not the main problem. You stated that some areas are smooth, and some other areas are rough. So that puts a question as to the possibility of some scaling that you might be dealing with.
If the blotchy gray areas were calcium scale, simple sanding would easily and immediately remove the discolored scale. And ascorbic acid treatments might also remove recently formed scale on brand new plaster.
IMO, the second photo appears to be gray mottling discoloration of new pool plaster. Gray mottling discoloration is within the plaster surface, and should be smooth (if the plasterers troweled the surface smooth in those areas). It is not a "deposit" type of staining issue that can be easily removed. Consequently, initial or light sanding won't remove the discoloration, but further hard sanding eventually will. So will a strong acid wash. But of course, that will also etch the plaster surface, meaning, that plaster material is removed in the process of performing an acid wash.
Gray mottling discoloration is usually caused by the combination of overly late hard troweling (in various areas of the pool) and adding too much calcium chloride to the plaster mix.