I have a customer that, once we got the pool clear, had a looonnnggg brown (-ish) stain that went down the pool's floor from the spa spill-over to the drain. This was a pebblesheen pool. Initially, it looked like algae, but what happened (apparently) is that the whole pool deck, spa-spillover, "tile" and coping are made with this reddish flagstone.
After having another pool guy look at it - we agreed that it was likely iron.
After calculating that I would need about $50-$100 in ascorbic acid, the guy at my distributors handed me the Hasa Stain Treat (~$20 retail). I figured it was worth the try.
I turned off the SWCG on Friday, then on Monday stopped circulation and poured the whole quart over the stain area. I expected very little impact/effect. Customer re-started circulation the next day.
Today, I stopped by and, I was wrong (don't tell my wife you hear me say that). Not only was the whole stain gone, but all the pebble looked "better"...
For ~$20 retail - I'm very, very impressed.
(AND YES - I KNOW THIS THREAD IS WORTHLESS WITHOUT PICTURES...)