The 3 best methods i have found are glass bead blasting salt blasting and soda blasting.
Best swimming pool tile cleaner.
If the dirt and grime at the water line is minimal scrub at it with a used toothbrush and one of these cleaners.
We like plastic scrapers because they don t scratch.
For in ground pools one of your best options is the hayward 2 wheel poolvergnuegen pool cleaner which is specially designed to deliver maximum power no matter how powerful your pump is and suck up large debris.
A scraper to help remove thick calcium buildup as you soften it with your tile cleaner of choice.
If you prefer to try a chemical free method whenever possible there are a few cleaning agents you may already have without having to go spend more money.
Speed cleaning s scum bum which is safe to use on pool tile works great to remove calcium at the water line and it will even break down thick calcium buildup.
They use high output low pressure stream to clean the tiles.
1 glass bead blasting uses a stream of ultra fine perfectly round glass beads about the size of a needle tip 10 microns to clean the calcium oil and grit off the tiles and grout.