I've had my pool for about a year (it's ten years old), and finally decided to deal with what I believed are rust stains on the bottom. My chems always test perfect by Leslie's Pool, but it wasn't maintained very well by previous owners.
I scrubbed some of the spots off with an abrasive thingamabob that the pool place recommended. It worked in the shallow end, but I couldn't get enough leverage in the deep end to make any progress. Today I tried putting a few vitamin C tablets on a few of the worst spots, and they turned black without diminishing in size. Does that give any of you an indication of what I'm fighting? Any advice would be greatly appreciated.