Really enjoy this forum.
I, like many with "pool questions" inherited a beautiful 20k in-ground plaster finished pool with my new house in central Virginia. The pool underwent an overhaul about 1.5 years ago with a new plaster finish and brickwork/tiling around the edge of the pool.
I opened the pool this year with a high pH (~8.0 per ColorQ) and low CH (~120). I threw some calcium chloride in to raise the CH to about 180. Other test results: TA ~60, CYA 40. Water was pea green so i shocked with liquid bleach and did a whole lot of vacuuming per instructions on this board. Pool cleared up nicely and I am adding about a 96oz jug of bleach every other day while waiting on a SWG to be installed.
I have several areas of widespread discoloration... some patches on the sides of the pool, but primarily on the bottom. In particular around where my two returns enter the pool (I have none on the side and three returns plus a main drain on the bottom). The entire bottom surface of the pool has a relatively rough feel.... not terrible, but kind of like a fine grit sandpaper - not really actually bothersome other than the discoloration since it gives a little bit of traction. It doesn't seem to be better or worse where the discoloration is. Ironically the surface around the water line is very smooth but further down gets somewhat rough.
Current test results are:
TC - 3-5
pH 7.2-7.4 (presuming this is calcium scale, I've lowered the pH to this level)
TA ~80 (assuming it increased due to liquid bleach)
CH ~120-140 (this is with the Color Q... I actually can NOT get the test to register with the Taylor drop test...).
So I had been operating with the assumption that this is scale, but I read today that etching can also cause tan brown stains. So I'm a little freaked out by that since the plaster job was new and I guess this is possible with the low CH... will post some pictures later. The stains definitely look more pronounced in the shade.
My main question is: etching vs. scaling. My second question would be what is the proper CH balance if you ARE fighting scale? I don't want it to drop too low, do I?
Edit: I should add that I do not know what the readings prior to closing since we moved in after the cover was on. The pool guy who did the plaster job did warn me about high pH over the winter but having absolutely no clue about what I was doing I added some muriatic acid blindly about halfway through winter and just swept it around as much as I could with a pool handle vacuum.