Blimey. I’m glad you posted this!!! We were all set to drain ours this winter because there is a lot of calcium deposited from the hard water here (greater than 400 ppm!!!) on the tiles. I was going to acid wash and re-grout to smarten it up. It’s so bad you scratch your skin if you drag a leg along the bottom!!! So what do you do if you can’t drain down???
If you know that you won’t have a water issue, you can drain and clean, refill the same day or the next day. Otherwise, drain some water and do your cleaning and then refill. You can also use acid with water in the pool and a stain/scale remover there are often treatments you can put in the water that will help. Good luck!
We have had some success with magic erasers. Use caution and test in an out of the way spot first to make sure you won’t scratch or damage your pool surface.