Split into a new topic. Please, only ask new questions in your own topics. JasonLion
Sorry to bump this but I'm dealing with a glass tiled pool at the moment with similar stains. I'm meant to be cleaning and regrouting this pool for a client. The grout has completely gone. I've emptied it and at the waterline there is a wide tide mark, partly white partly white. I guessed it was iron and calcium as the pool is filled with well water and is 30 years old. So far I've managed to remove the white with 10% MA undiluted, wiped on with a sponge without using too much so as not to loosen the tile adhesive underneath. There is some fizzing but not the characteristic yellow foaming. The brown is almost impossible so far. It even resists a wire brush attachment on my angle grinder. I was unable to get pure Asc.acid but I got 100g from a pharmacy which also has sucrose and a few other things in it and this did nothing at all. I also tried neat bleach, mechanics hand wash product (thinking maybe it was suncream residue) and MEK (pool plumbing cleaning solvent).
The residue is hard and the only way I've got any off is by using a chisel on a very small area.
I'm going through all the results of my searches here but I wondered if anyone has any more ideas?