On Monday I performed an iron treatment on my 10,000 gallon 15 year old pool, in the past (three other times) I have used ascorbic acid from a chemistry store and un-buffered Vitamin C from the local health store in all cases using about 1 lb 8 oz. The results were good but still left some staining.
This time I used 1 lb 12 oz of "Natural Chemistry's Stain Free" (Note: I have no relationship with them) and no sequestrant completely draining after 12 hours, at 7 am in the morning. The results were spectacular all stains were gone, save a very few which I scubbed out. The pool looks in near new condition, it is about 15 years old.
I do not know why this product worked as well as it did.
Three further comments that might help to avoid algae blooms.
One: I noticed in some other posts that an algae bloom occured with some people that did and did not use Polyquat 60 Algaecide either during treatment time and/or the refill, I think one should always use it when the chlorine goes to zero. I think it is wise, prior to doing the stain treatment, to bring the pool up to high shock levels.
In my case with a CYA of 30, I brought it up to 24 ppm of chlorine for four days before treatment, then lowered it to 10 after two days or so, and then used Thio-Trine to drop it quickly to zero, then I added Polyquat 60, running the pump for 4 hours to mix, prior to dumping in the ascorbic acid.. This I think helps to further avoid the issue of algae blooms after the treatment, providing as it does some additional insurance. Polyquat 60 is still an absolute must on the refill to my mind.
Two: Scubbing the walls and floor of the pool twice a day for four days prior to treatment also helps a lot. And yes it is a pain especially if your are at my grandfather age.
Three: It is very important on the refill to keep the chlorine level up, say around 4 ppm at a CYA level of 30, this is easily done with a SWG running 24/7 for a few days, I do this. Even though I do full drain there must be some ascorbic acid left in the pool as the chlorine gets used up very quickly, also the Polyquat 60 uses up some of the chlorine.
Attending to the chlorine level upon the refill is much harder if you are using the BBB method and go to work in the daytime, I did this in the past, best then to do the refill on your day(s) off. This is case where adding the new type near instant liquid CYA is worth buying. Here in Honolulu the price difference between regular granule and instant liquid is not that great.
Hope this helps.