Stop adding bleach.
Your FC is way too high.
The FAS-DPD can only really test up to 50ppm.
Given your volumn of 6400 gallons, and a CYA of <20, your slam level is about 10ish, or slightly less.
2 gallons of 8.25 bleach will raise FC in 6400 gallons by 25ppm.
And this has been going on a few days? Even with algae, its reasonable that only about 1/2 of the 25ppm a day you have been adding is being consumed. So the residual FC each day has been adding up.
You need to let the FC come down. Dont add any more bleach. Dont add anything until you can get back to a starting point where you accurately measure FC.
Test your water on Sunday, if the fC is higher than 15ppm (30 drops), then stop testing and save your test regeant.
Do a test each day thereafter until the FC comes down to 15 and then lets go from there.
Once your FC reaches 15, add enough CYA to get that up to 30. Use pool math to figure out how much CYA to add to reach that level.
Dont worry about testing the CYA after you add it. It takes a week or so to show up on the test.
After you added the CYA, then test your pH. If its higher than 7.2, then add enough muriatic acid to lower the pH to 7.2. (I suspect it will be high)
However if by the slim chance pH is 6.8 or below, use Washing SODA (not washing powerder). to raise the pH to 7 - 7.2
When you have achieved that, then continue to SLAM. With CYA of 30, your new FC slam level will be 12ppm.
hope this helps,