12,500 gallons=>9.6 PF
10% shock => approx 0.8 lbs chlorine (gas equivalent)
0.8 x 9.6 = 7.7 ppm

2 questions:
1. What is PF?
2. Is 7.7 ppm the chlorine that the 1 gallon of 10% sodium hypochlorite will add to my 12,500 gallon pool?