A 24 round x 52" will hold about 13,500 gallons; if it's 48", it will hold about 12,500. You were probably told more than that, because AG pool companies figure volume at the 'running over the sides' level. Anyhow, the pool industry has no particular definition for what it means to "shock a pool", so I can't answer that question.

But, I can tell you that each gallon of PLAIN 6% household bleach (watch out for the 3% bleach sold by Dollar General and others) will add about 6 ppm of chlorine to a 12,500 gallon pool and about 5 to a 13,500 gallon pool. If your pool has algae, a reasonable dose would be 2 gallons of 6% each EVENING, till no algae is left.

For more information, read the "Best Guess" page (linked in my signature). If you want to take care of your pool yourself, and not buy all the pool store goop, read the test kit page (also linked in my sig), since you'll need both an OTO kit, and a K2006.