I am currently 3 hrs and 23 mins into draining my pool for the first time. The pool has only been in operation for 1 year since it was resurfaced (pebble finish). I used a pool service for the first year (so many puck has been used for chlorine). The pool has an attached spa, but it has never been used as a spa (we don't have a heater).
Once the water level came down to a certain point, a nice rust-color stain is now apparent. The stain's upper most border is the pool's water line and its left and right borders are on the outsides of where the water spill-over occurs. Notice there is no staining on the corner of the spa (since no water spills over in that location). So, it seems the spill-over water is causing the staining.
Does anyone have a guess as to what is causing it? This may be unrelated, but I cleaned my cartridge filters for the first time last week. The filters cleaned up nicely EXCEPT for 2 of the 4 filters had a 12 inch area of rust-colored staining on them. So, the filters were clean of debris, but the stain remained. This staining appears no where else in the pool.
Thanks in advance for any guesses or recommendations on what to attempt to clean it with (as to not harm the pebble finish).