I was at a friends house today and that have limestone or flagstone around the pool and patio area, about 500 sqft. There's white alkaline build up on it, at first I thought for sure chlorine, but a lot of the build up was 20' from the pool on the patio area. I cleaned the cabana 5 months ago and my helper spilt my HF, but I washed it down right away, I thought maybe that got in there? Either way, the owner said he tried I believe muriatic and phosfuric acid and nothing. What can I use? No...
What type of acid?
What type of acid?