Keep that FC up, but do NOT use Di-chlor powder or Tri-Chlor tablets, and certainly not the HTH sticks. Stick to bleach or liquid chlorine. With your CYA that high, once you kill the algae, you'll be able to maintain a residual FC level easily, probably best to keep it close to 15, and won't have to add much bleach at that point.

If your CYA is really that high, you can safely bring your shock level to 30 or 35ppm without damage to your pool.