Probably within the first couple of days after filling I noticed that the tile had a lot of "stuff" on it, like leftover mortar. I also noticed that the same "stuff" is on the surface of my LED light. Somehow that doesn't seem normal.
For us to rule out scale, we need the current test results. If you can scrape off a piece of scale intact, put it in a plastic container and pour a little MA on it to see what happens. If it is scale it should fizz and dissolve.
My target FC is 8 and I keep it around that, CC .5 this morning but normally 0, I keep PH below 8. This morning it was 8 and I put in some MA to bring it down to 7.5. TA 90, CH 250, CYA 45. Water temp is about 70.
Your Calcite Saturation Index (CSI) was never very high and is the highest now at around +0.3 units. So it seems unlikely that the scaling is from your water chemistry during the period of time you were managing it. I'm guessing that you are right that this may be something from installation such as mortar rather than calcium carbonate scale. It's possible that the mortar curing got the pH and CH very high locally and caused some scaling but fresh scale should be removable by acid without too much trouble and you did not find that to be the case.
Try going with a stronger mix of acid and see if that helps. I had some scaling below the rock wall on the far side of my pool within a few weeks of the first fill and it took a hefty amount of 1:4 MA to take it off. However, when I sprayed the MA on it, it would bubble and fizz, so I knew I was on the right track.
I had scaling on 4 or 5 limestone wall rocks. I used 50-50 acid-water, gloves, and stiff nylon brush. Dissolved quickly. Don't think my chemistry was ever off too far (although I find it difficult to keep pH below 7.8-8).
That is just leaching from the mortor and grout. Agree with tcat above just use 50/50 muratic acid/water and the stains will dissolve. I was told by my PB this is totally normal for new pools. After I cleaned some of my tiles the stains have yet to reappear.
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