We recently took over a pool - it's a 20,000+ gallon salt pool. When I took the pool over, the salt level was around 1800ppm which was too low for the unit to work properly (it has a 40k purechlor system which requires salt to be in the range of 3500ppm - 4500ppm). In any case, it's a beautiful pool with a relatively new surface (about 3 years)... the surface is very similar to a pebble tec finish (home owner wasn't sure the exact type of surface). The home owner is VERY particular... she fired the last pool company because she was getting small calcium spots on her pool. When I took the pool over, I lowered the PH to 7.2 and the alkalinity to 60 to make the water a little more aggressive... then I added a sequestering agent. In a week or so, I was able to brush off the calcium spots. Also, I slowly added salt to the pool to bring it back up to normal level (3850ppm now).... over the last few weeks, a very lightly colored white-film (almost looks like sunlight) is spreading on the bottom of the pool. I'm keeping the water aggressive and brushing it down hard. I put acid directly on the film but it doesn't really do much... The home owner is not happy, however, the water chemistry is perfect so it's hard for her to blame us..... My guess is the pool's surface does not react well with salt and some type of scaling is happening due to high saline levels in the water. Also, now I'm seeing those calcium spots reappear (even though the water is aggressive and the calcium level is 270)... very strange problem and nothing seems to help to take off the film. The pool builder (who did the surface 3 years ago) recommended to the home owner to drain the pool half way and dump 8 gallons of acid in the water. I would rather not do that.
Stain treatment is not really my strongest area of expertise.... hopefully, someone here has a better idea of what this is and/or how to handle it. Thanks!!!