Each gallon of 12.5% should raise your FC by approx. 4.8 ppm. In order to attain shock level, you need to know your CYA (see the link to the best guess chlorine chart in my sig for more info and for the chart). If your CYA is 0, then you'll need to reach 12-15 ppm of chlorine in order to achieve shock level. If you have green in the pool, you'll need to reach and maintain shock level until it clears.

Can you break off a piece of the scale? If so, put it in a covered jar with some white vinegar overnight and see if it dissolves. If so, there are folks here on the forum who can instruct you in what's needed to dissolve it back into your pool water, but definitely don't use any cal-hypo for chlorination until that's addressed.