WOW! That is some bigtime CYA! The only way to reduce is to drain, but you don't always want to do that. Depending on the type of pool and level of water table you can either destroy a liner or float a pool out of the ground. Give some more information about your pool.

Having said that --- how did your dealer measure your CYA? Did he use a disappearing dot test? Even if he did, the test cannot differentiate values over 100. Did he dilute the sample?

We need more info .........