Your CYA got as high as it is from the use of stabilized chlorine like trichlor--with trichlor, for ever 10 ppm of chlorine it adds, it also adds about 6 ppm of CYA, so over a 2 year period it can get quite high.The only way to lower it is through water waste (splashout, frequent filter backwashes, partial drains, etc). It will come down, eventually, if you do not use any more stabilized chlorine, but it will be very, very, very slowly. You can do several partial drain/refills to help it along without hurting your liner too much, but if you completely drain the pool, the liner will float and will not be able to be refilled, in most cases, which is why Pooldoc stated that #1 above wouldn't be recommended. However, you could drain some of the water--a foot or two at a time, and refill that, and shouldn't hurt anything.

For more information on 3 and 4, take a look at the best guess chlorine chart linked in Pooldoc's sig above. It will explain the chlorine/CYA relationship and specify where your chlorine levels will have to be in order to run the pool with the CYA that you have.

Regar