I didn't see a category where this thread should go so mods please move it to its rightful place. Anyway, we had our pool installed exactly 10 years ago. 15x30' 17k gal. concrete with a Florida Stucco Gem finish. I've been doing the BBB method from day one with success. Two years ago we had way too much rain (alkaline) and I allowed my PH to rise a bit too high and some iron staining occurred. It was mainly just some darker areas. Last Summer I tried the ascorbic acid treatment as detailed on TFP. I ended up with clean splotches all over. (see attached pic taken today) That issue was minor and on the back burner. A couple of weeks ago when the CL shortage hit, I decided to make the switch to SWCG. I ordered the salt test kit but before it came in I thought I'd be safe adding 66% of what the chart said. I thought wrong and I ended up with 5600 ppm salt. I calculated a 28% drain and refill to get the salt right and started that this morning but thought this would be the perfect time to acid clean especially when our ground water levels are at a record low. It has never been cleaned. So, all that said, is muriatic acid safe for the Gem finish and if so at what concentration? Thanks for reading!