I am a new user to this forum and I am very hopeful I will finally begin to get a handle on taking care of my pool. I started to prepare my pool for summer about a month ago and as is typical it was green. I shocked it, cleaned it, etc but it just would not clear up no matter how much I shocked it. After finding this forum, I got a good test kit and when I measured the CYA it was basically off the scale. My test kit measures by mixing a reagent and then dropping the solution into a vial with a black dot at the bottom and when you can't see the dot you look at the scale to determine the ppm. The scale starts at the top and reaches 100ppm at about half way down. I couldn't see the dot at about 1/4 full (half way to 100), and looking at the scale, it is not a linear scale so I don't really know where my CYA is. What I can't figure out is where it came from. I have not added CYA and I refilled the pool completely the beginning of last year. I have only used regular chlorine tablets and shock since refilling as well as pH+ a couple of times. Here are the results of my tests:

TC = 4 (top of scale)
TA = 90
pH = 6.8
CYA = >100

The pool is 18,300 gal

Any assistance would be appreciated although I am pretty sure at this point the answer is going to be "Drain it and start over!"