Just did a pool remodel and upgrade. The workers did not wipe up the excess tile grout very well while it was still wet. I have many areas on the tile faces and coping edges where there is hard dried on grout. Tried to remove with a wire brush, but didn't work very well as the dried grout is that hard and was afraid of scratching the coping edges (travertine). Thought about using a muratic acid solution, but thinking only on the tile as I'm guessing that it should not be used on the travertine coping edges. Any thoughts?