It looks like you need to get HEDP. I didn't realized the old Monsanta Dequest brand was still active; it's now owned by ThermPhos, and is documented at www.dequest.com. Any how, the properties I could find for Dequest 7000 (2-phosphono-1,2,4-butanetricarboxylic acid) mentions calcium scale inhibition, but not heavy metal sequestration or chelation. Usually, if a product desired property is NOT mentioned, it's not present.

Let me caution you that the stain removal process is VERY sequence dependent; do things out of order, and you can end up wasting all the chemicals you bought!!

Dequest® 7000
Title : Dequest® 7000
Synonyms : 2-Phosphonobutane - 1,2,4 - tricarboxylic acid
Cas number : 37971-36-1
Einecs number : 253-733-4
Product grade : Industrial
Description : Excellent Chlorine stablity and calcium scale inhibition in high stressed alkaline conditions.
Applications : Controls scale where halogen-based biocides or hypochlorite bleach are employed. Controls calcium scale formation in high stressed alkaline conditions.
Storage : Material should be kept cool and dry for best results.
Shelf life : 2 years
Packaging : Drum; Tote; Bulk
Safety : UN 3265 CORROSIVE LIQUID, ACIDIC, ORGANIC, N.O.S., Class 8, PG III


Dequest® 2010
Title : Dequest® 2010
Synonyms : 1-Hydroxyethylidene -1,1,-diphosphonic acid, HEDP
Cas number : 2809-21-4
Einecs number : 220-552-8
Product grade : Industrial
Description : Dequest® 2010, noted for its excellent CaCO3 scale inhibition and chlorine stability is based on hydroxyl ethylidene (1, 1-diphosphonic acid) and is approved for applications in which boiler steam comes in contact with food.
Applications : Noted for its excellent CaCO3 scale inhibition and chlorine stability. Only Dequest® approved in boiler steam contacts with food. Cooling water treatment, boiler treatment, I & I Cleaners, swimming pool, stain prevention, metal ion control.
Storage : Material should be kept cool and dry for best results.
Shelf life : 3 years
Packaging : Drum; Tote; Bulk
Safety : UN 3265 CORROSIVE LIQUID, ACIDIC, ORGANIC, N.O.S., Class 8, PG III
Manufacturing site : Newport