I'm dealing with a little staining again this year and needed some more Jack's Magic The Pink Stuff to sequester after using some ascorbic acid, plus some for maintenance dosing.
Locally The Pink Stuff sells for around $24 a quart. I've felt lucky to order it for $19, $10 handling and free shipping in past years. It adds up when I need 3 quarts initially then about 16oz a week as a maintenance dose to keep my stains away. I slack on the maintenance dose however.
Good news is I found a new site : 4guyspoolsupply.com
They don't seem to have a lot of chemicals but they do have a lot of parts it appears!
I'm happy to find my sequestrant at a much better price ($15.05 a quart) even with paying shipping. I'll check them out if I need any replacement parts for sure.
I still think Mbars link for the ascorbic acid is the best deal around and it works great!