So, full disclosure time. (No judging, I promise. You didn't know better at whatever point, possibly for years.

).
How did you get metals in the pool ? It's likely not iron unless your home plumbing is ancient. Copper didn't come from your municipal water, but would from an ionizer (possibly long abandoned) or a host of typical pool products like algecide or Xtra blue tabs. Much of the Walmart aisle for example will add copper. Everything blue this or blue that.
My hope is this fixes itself at regular range FC and with no staining (but clearly metals which took a long time to build) you can maintain blue water while you liesurely work on exchanging some water to bring you below the threshold where it appears as it did. You may even be able to wait it out for rain to do it for you if we have a wet summer. Or it's still less of an emergency if you have to do it manually.
If it doesn't clear, it forces the need to drain immediately and the amount needed is a total guess. Some metals, say a .2, is fine. Again with no staining I suspect you're closer to ok than not. But a 1 ft drain may not do enough and you'd need to do another. That'll be for you to weigh out and decide if we end up there. Subsequent drains remove good water with the bad, so ideally we get it right the first time.