If you are thinking of using powder based chlorine to shock the pool, most folks in this forum will warn against it... powdered chlorine is stabilized which will add CYA to the pool. Some powdered shock contains calcium, some contains copper, some is based on MPS. So using any of these to shock the pool can cause additional problems.
The chlorine form that has the least additional byproducts is liquid chlorine, or bleach. It's cheap, easy, and effective, and you minimize additional chemicals in your pool.
Good luck!