Only choice is lifting the iron using Ascorbic Acid Treatment - Further Reading then replace the water with metal free water.I think that works with heavily contaminated (brown water) but doesn't take out the sequestered iron that I have!
What I was suggesting above was to lift the metals into the seqestrant and the drain the water out and replace it with metal free water.I've tried that, it means adding chemicals to keep the metal suspended.......for ever!
There are many risks to draining a liner pool, depending on the age and brittleness of the liner. In general we don’t recommend draining a liner pool totally. Leaving some water in the bottom of a liner keeps it from shifting. But for you it leaves some metals in the remaining water.There is a solution somewhere, the only other method would be to drain the pool, clean the liner with an AA solution and refill?