Since you already bought it, you can go ahead and use it up if you want. But, it will not add CYA (which the dichlor will) so if you do use the cal-hypo, you can just buy some CYA and add it separately. You may be able to find it at Walmart or you may have to get it from a pool store. Sometimes it is labeled as conditioner or stabilizer. Check the label. If it says cyanuric or isocyanuric acid, that is the right stuff.

If you decide to get some dichlor, you will not need to purchase the CYA separately.

EDIT: It appears that Ben and I were posting at the same time.