HTH Dual Action lists the following ingredients:
TRICHLORO-S-TRIAZINETRIONE 87-90-1 90 - 96
Copper Sulfate pentahydrate 7758-99-8 1.4 - 1.55
Aluminum Sulfate 17927-65-0 4.5 - 4.9
Is that what your container lists?

I can find 'HTH 3" Chlorinating Tablets' at Walmart:
http://www.walmart.com/ip/HTH-3-Chlo...blets/21002455'

Is that what you have? I can't get a label or MSDS for that, so you'll have to read it and tell us what it is.