Happy to be wrong

And yes, when cleaning up the pool water, the chlorine titrating reagent goes FAST! I always keep a spare 2oz bottle in reserve. I hope you're using the 10mL (0.5ppm/drop) water sample size? That will save you on reagent.

Cooler weather is a big help. The algae, if present is less active and doesn't reproduce as fast.

One other point which I hope your aware of - all pumps/water features should be running while you do this. You want to make sure chlorinated water is reaching every part of your system and you should leave the pumps running for 24 hours while you wait to test again. In fact, you should dose again this evening after sundown to get your water back to 20ppm and then measure again in the morning before direct sun is hitting the pool to see what your overnight chlorine loss is. If, by morning, your water is clear, your CC's are 0.5ppm or less and your overnight loss of FC is less than 1ppm, then you are good to let the water drift back to normal FC.

Be sure to keep an eye on your filter pressure as well. After all is said and done you'd probably want to give it a good backwash to clean out any accumulated dead junk.