IMHO, you need to keep putting chlorine in there. What type of test kit are you using for FC and TC? Is it DPD (comparator cell with pink colors) or FAS-DPD (titration test)? The reason I ask is that DPD can bleach out with high chlorine levels. I don't think this is what is happening. I think you just have a big chlorine demand and the only thing that will take care of it is to satisfy your pool's "hunger" for chlorine right now but it is one possiblity that sprung to mind to explain your FC of 0. Bleach is NOT your only alternative. You might want to check around at the prices of liquid chlorine and cal hypo vs. bleach. Sometimes they can be a bit more economical (but usually not). Your CH is at the high normal end for a plaster pool but your TA is on the low side so I don't believe that cal hypo will be a problem. I personally would stay away from stablized chlorine with your CYA levels being as high as they are.

As far as polyquat, have never used it but my understanding is that it is more of a preventative than a treatment from what I have read on here.

Hope this helps. Keep the faith, you WILL be swimming soon!