Help removing calcium buildup on tile

Apr 25, 2017
Bought a house with a pool. My first pool and unfortunately it has not been taken care of all. Chemistry is all out of whack which I am working on. It is about a 13k plaster pool and spa with a SWG. Ca is close to 2k so I know what the problem is. I am draining the spa as I write this to remove some brown stains (and start to dilute my off the chart chemistry). I worked on one tile for over an hour. I used muriatic acid and Bio Dex 300. I used soft brushes, steel brushes, chisels and finally a straight razor (I know the risks). I do not want to have someone come out and drain the pool, blast it, and have more problems than I do now--I really don't (if I have learned nothing else, it have learned--trust no one). Any ideas? It is about 3/16 inch thick. When you spray muriatic acid on it nothing happens (no fizzing).

After two weeks I think I have a lifetime of stories! Can't imagine the stories the rest of you have.