I'm switching over from Pristine Blue (copper) and after-use shock with Dichlor to the TFP system with BBB for my 250 gal hot tub. The tub is currently quite clear and clean, getting almost daily use.
I've been reviewing 'Pool School' recommendations. Playing with the 'pool calculator' by entering arbitrary numbers, I noticed that the recommended amount of bleach to raise my FC from 2 to 6 (for example) was no different if I entered a CYA of 0 vs a CYA of 60. TFP stresses CYA testing because a higher CYA would require more chlorine for adequate FC level, if I understand correctly. Does the pool calculator adjust its chlorine advice for different CYA's or are they independent variables?
Seems like the CYA level helps you choose an appropriate goal FC range. But the difference in how much bleach to add at different FC goal levels for a 250 gallon volume is minimal, tenths of an ounce. I'm tempted to not bother testing my CYA level (bought as a separate test kit it's about $17) and just pick a reasonable FC range that assumes some CYA present (I've been shocking with Dichlor, which you say adds CYA, the spa gets no direct sunlight).