Sorry I hadn't picked up on this sooner.

You are almost certainly experiencing the well-established problem of cyanuric acid conversion to ammonia or urea by bacteria. This results in the HUGE chlorine demand, and high CC levels, you are seeing. There are only two solutions: (a) drain and refill - NOT safe on vinyl IG pools, OR (b) chlorinate until the demand is gone.

You can use the bucket test BigDave described to answer, approximately, the question, "How much more chlorine will it take?". Or you can just chlorinate till it's done.

For a variety of reasons, you are probably better off doing this at a higher than normal pH, but you can't go very high with Alk and CH over 300 ppm. So, I'd recommend using borax to push the pH to ~7.6, and holding there till you get the situation under control.

Do NOT swim while you are doing this. High chlorine is rarely a problem for people, but high chloramine levels are something different.

Adding CYA will slow the process at this point. My recommendation would be to
1. Use borax to raise the pH to 7.6, and hold it there.
2. Dose each evening with 4 gallons of household bleach UNLESS the TOTAL chlorine (FC + CC) is greater than 20 ppm. Skip doses when TC levels are above 20 ppm.
3. Use the bucket test if you want to find out how much longer you have to go.

Sorry about this. We had many, many cases last year, with the super-warm spring of 2012. This year, with a record cold spring, there have been very few cases.