1. List exactly what you've got -- brand name, % ingredients, product name, so we can see what you can use.

2. If it was empty all winter without problems, it's probably safe to drain.

3. Dichlor is sodium dichloro-isocyanurate -- equivalent to trichlor (probably the main ingredient in your pucks), but less chlorine and less acid. Both add chlorine and stabilizer and lower pH.