You need to know how high the CYA level is, and most tests only read up to 100 ppm. It is possible to have CYA at 200 or more. While it is possible to shock and clear a pool with very high CYA, the cost to do so would be high. You need to find out how high your CYA level is so you will know how much bleach to use to reach shock level, and how much bleach would be too much.
Use a mixture of 1 cup pool water and 1 cup tap water and test the CYA level. Double the result. If your results over 70 ppm you should partially drain and refill the pool to bring the CYA level down.