Your current chlorine is 7.86%? How did you get that? Chlorine levels are measured in ppm (parts per million).

With a CYA of around 30, aim to keep your chlorine around 15ppm until you meet three criteria:

1) You lose no more than 1ppm of FC from sundown one evening to within one hour of sunrise the next morning
2) You have no higher than 0.5ppm of CC
3) You have no signs of algae

Don't worry about buying muriatic acid at this point. You don't currently need it. Your pH is fine at 7.6.