I think I see something: Your CYA didn't rise because it takes 48 hours to a week for the CYA to dissolve properly...and if you've been vacuuming to waste you may WELL have vacuumed up and out the undissolved CYA particles.

You've got a gunite pool. If it were me, I'd get a 5 gallon carboy of 12.5% liquid chlorine and dump in 2.5 gallons. That should raise the FC by about 30ppm, which may just make a dent in the algae. 8 hours later, I'd check FC again, and if it dropped, I'd dump in the rest of the LC. Gunite/concrete/plaster can tolerate such high levels, unlike vinyl.

When you use the OTO, are you diluting it with steam distilled water? If not, look up the Shot Glass method. Mix one shot of pool water with one shot of distilled, and you can double the readings. Two shots of distilled to one shot of pool water and you can triple the reading. 3 shots distilled, quadruple. Beyond that you will probably be losing accuracy.