(NOTE: This thread is in The Deep End because the following product has not been tested yet to be proven to be effective by members of this forum -- the product is fairly new only being introduced in February of this year.)
I just found out about a new product called CuLator® Metal Remover. It's not cheap at around $30 for a one-month supply. Their FAQ document states the following:
So that can clearly get pretty expensive if one has a lot of metals in their pool. 0.5 ppm in 20,000 gallons would cost around $150 if there is only one bag in their 1-month supply box, but it would be a one-time cost unless metals were getting re-introduced into the water, though that could get handled by other "metal trap" products (ion exchange resins) on fill lines. [EDIT] As Jason notes below, there are two bags in the box, each for 2 weeks, so that would be $75 to handle 0.5 ppm in 20,000 gallons. [END-EDIT]Dosages are dependent upon the level of metal ions in the pool. One bag will bind 1/3 of its weight in metals. This large capacity, relative to other chelation and sequestering agents, is why such a small amount of polymer is able to bind so much metal. In terms of pool water, one bag will lower the metal level of a 10,000 gal pool by .2 ppm (or .2 mg/L).
Instead of just sequestering metal ions in the water, it has a polymer that has the metal adhere to it so when you throw out the bag you are physically removing metals from the water. After I find out more, I may do another ascorbic acid treatment in my own pool and be aggressive about removing some iron metal stains, but will use this product to remove the metal from the pool. I may also use it periodically for maintenance though likely not at the frequency they recommend until I get the rusting iron source fixed from the stainless steel bar mounts in my pool that rusted years ago when I used Trichlor.
If anyone has a serious metal problem and doesn't want to keep adding sequestrant, then this might be a product to try. Of course, there's no guarantee it will work though the reports on Amazon are so far favorable (assuming those are real users of the product). It's available on Amazon, but not too many other places.