I got this information today from Jack's Magic and LaMotte and thought I'd pass it along.
Jack's Blue Stuff is better than their Pink Stuff if you have copper stains. (I have both copper and iron stains, from a still-unknown source.)
Jack's Blue Stuff is an organophosphate metal sequestrant, which is not a nutrient for algae. The Blue Stuff can break down into an orthophosphate, which is a nutrient and can cause algae blooms (unless chlorine levels are kept high enough).
Some phosphate test kits test for both organophosphate and orthophosphate, and if you are using an organophosphate metal sequestrant this can yield crazy-high readings that don't drop even with a phosphate treatment.
The LaMotte phosphate test kit only tests for orthophosphates.
Doing a phosphate treatment will not degrade the organophosphate metal sequestrant in Jack's Blue Stuff. The phosphate treatment will remove the orthophosphates.
LaMotte has a test kit for metal sequestrant levels that is less than half the cost of the test kit sold by Jack's. (Part no. 4064-01, around $40 online.) Jack's recommends that the sequestrant level be tested weekly and raised to 12 ppm if necessary. I would expect that the savings from using the test kit vs. Jack's standard recommendation of 6-8 oz./10,000 gallons/week would pay for the test kit.
You can get a kilogram (2.2 pounds) of pure ascorbic acid from multiple vendors on eBay for around $18 with free shipping. TFP recommends half to one pound of ascorbic acid per 10,000 gallons.
I tried the CuLator (http://www.CuLator.com) product this summer to try and physically remove the metals from the water (rather than just keep them suspended with the sequestrant), but I don't think I was using enough or the right kind of sequestrant to carry the metals to the CuLator. I'm going to install a new CuLator as part of my upcoming AA treatment+shift to Jacks' Blue Stuff and see what happens.
CuLator recommends the following sequence of events: Install new CuLator, perform AA treatment, add sequestrant.
The CuLator Ultra Powerpak 4.0 has 4x the product for around 2x the price of the 1.0 Powerpak. The Ultra Powerpak also comes with a plastic "egg" that allows the CuLator to be placed in the lint basket to maximize the water flow over the CuLator. I've only been able to find the Ultra Powerpak online.
I'll probably put the used CuLator "egg" in a skimmer to get as much use as possible out of it.
(Weird side note. Just by chance I've done my AA treatments in the later afternoon, and the stains have not fully been lifted. The next morning, as soon as full sunlight hits the pool, the stains disappear within a half hour. This is true for surfaces in both sun and shade, so it appears that something in the sunlight "activates" something about the ascorbic acid in the water.)