Hi, and welcome to the forum!!
In order to kill algae with a high CYA, you just need to up the chlorine level based on the CYA (see the best guess chlorine chart linked in my sig for more info and the chart). Basically with 100 ppm CYA, this means you need to raise your chlorine to 25 ppm and keep it there by testing and adding more chlorine (we use bleach for this) as often as you can, until the pool clears and you can go from one night to the next morning before sunup without losing more than 1 ppm of chlorine.
If you'll tell us a little more about your pool, particularly your volume, and post a set of test results on your water taken with a drop-based kit, along with a list of what other chems you've been using, we'll be glad to help you figure doses or offer whatever help you need.
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