I started with a clean, clear pool with very high CYA and CH levels 240 and 1000+ respectively. Through pumping and rainwater dilution and one backflush, things were moving the right way. CYA 150, CH 550 at the lowest. I've been almost obsessive about keeping the pH and Cl correct
But then I started scrubbing these stains in the hot tub. Real elbow grease. The light spots are getting bigger. Good, hard brushing the walls and floor, especially one blotch in the shallow end that Ascorbic Acid didn't touch. It's fading.
And now my CH is climbing. Sigh.... I guess it stopped precipitating and is going back in solution. Nothing comes without a tradeoff.
So my new strategy is to keep the pH down at the low end and keep brushing to get as much scale off the walls as possible. It doesn't feel rough, it just looks ugly, so I may have a chance of removing it. And when it looks like I won't get any more off, bite the bullet and open the wallet and get the reverse osmosis treatment.