These hard water stains are from the previous owner not keeping the PH balanced, I believe. And they've never cleaned the tile in the 20 years that they owned the pool. I took a pressure washer to it, and it got some of the thicker layers off (you can see in the photo). I sprayed a 3 to 1 mix of water/muriatic acid on it, and it was smoking all over the white areas. But it's not helping much. I haven't tried a wire brush yet, but I was wondering if there is anything else I can do.
I'm currently draining and refilling the pool, so I'd like to make some progress on it before I fill it again.