For the convenience of other TFP-folk, here is some information that I obtained from Jack's Magic about their Blue Stuff metal sequestrant. (Their Pink Stuff and Purple Stuff have the same active ingredient, possibly just at different concentrations and/or with different additives.) Much of the information has been pulled together from several other posts I made. I've also included some of my own thoughts and later experiences.
The product support person(s) I've spoken with at Jack's have been very knowledgeable and helpful. The same is true for LaMotte.
If you are dealing with metal stains and using Jack's Magic Blue/Pink/Purple Stuff (or any other product with 1-Hydroxyethylidene-1, 1-diphosphonic Acid, aka HEDP, as the active ingredient) I would strongly recommend getting a test kit to measure the HEDP levels in your water. On the bottle of Blue Stuff the recommended initial treatment for my pool was 1.5 quarts. I ended up using 8 (!) quarts before the metal in the water was sequestered and I reached the target residual level of HEDP. Jack's also confirmed that the level of HEDP will drop gradually as it reacts with other ions in the water. With a test kit you will probably save money by putting in only as much HEDP as is needed instead of using the standard weekly dosage on the bottle.
LaMotte sells a Sequestrant Test Kit (Part No. 4064-01) for less than half the cost of the test kit sold by Jack's ($36-$40 vs. $98). I confirmed that the LaMotte test measures HEDP. The two kits appear very similar.
Jack's recommends raising the HEDP level to 10-12 ppm once a week. Absent an active source of additional metal(s) being added to the water, they would expect the HEDP level to drop by 4-5 ppm over the course of a week as the HEDP reacts with other ions (i.e. calcium) in the water.
Jack's said that the combined HEDP-metal molecules will be filtered out of the water by filter media that removes particles 10 microns or smaller in size. This would include D.E. and Zeolite filter media. Coarser filter media, i.e. sand, requires the use of a filter aid like D.E. or fiber. Once the HEDP-metal molecules are trapped in the filter, the filter can be backflushed and the metals physically removed from the pool water.
(Personal thought - If my metal levels stay at or near zero, and if my HEDP level doesn't drop more than the 4-5 ppm per week, I'll probably stop adding Blue Stuff and see if the metal levels start to rise. I'm not sure if I have an active source of metal(s) or if I'm cleaning up an old problem. I can save some significant money by only adding Blue Stuff if/as needed.)
Jack's said that Blue/Pink/Purple Stuff can withstand around 10 ppm of Free Chlorine (FC) for a short period of time, but higher FC levels, or longer periods of time, will "consume" the HEDP. If there are sequestered metals still in the water, they will be released back into the water.
A SLAM treatment will probably consume all the HEDP in the water, possibly causing staining and requiring that the HEDP residual be built back up.
It would be best to perform an Ascorbic Acid (AA) stain treatment after a SLAM treatment, rather than before. If you perform the AA treatment first, including adding sequestrant, the sequestrant will be destroyed by the SLAM treatment and the stains may reappear.
(Personal note - I learned this one the hard way, performing a SLAM treatment after an AA treatment - including $60 of Blue Stuff - and then having stains reappear. Luckily, after 8 more quarts of Blue Stuff, the stains disappeared again without having to perform another AA treatment.)
Jack's says that their Blue Stuff is better than their Pink Stuff if you have copper stains. (According to the Material Safety Data Sheets the active ingredient in both products is HEDP, so I'm guessing that the concentration is different and/or there are different additives.)
HEDP is an organophosphate metal sequestrant, which is not a nutrient for algae. The Blue/Pink/Purple 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.
Jack's said that doing a phosphate treatment will not degrade the organophosphate metal sequestrant in Blue/Pink/Purple Stuff. The phosphate treatment will remove the orthophosphates.