Ascorbic acid is one form of vitamin C, probably the most important one.
Food supplements sometimes also contain other forms like sodium ascorbate, calcium ascorbate or other mineral ascorbates (there are products that are 100% calcium ascorbate). Not sure how effective those forms would be for stain removal. Calcium ascorbate might have an impact on the CH level - I never dealt with removing stains, don't know if the required amounts would be sufficient to increase CH significantly.