CYA builds up over the course of the season as you use more trichlor. In some pools, but not others (no one really knows why), the CYA goes away over the winter. If your pool has the CYA vanish over the winter and your season isn't too long (so it doesn't get too high over the course of a single season) you might be fine.
If you want to know why you should believe us and not your pool builder you will need to spend some time reading this site and listening to the stories of people who have been "pool stored" and spent hundreds, or even thousands, of dollars based on pool industry advice and still not solved their problems. But that will take some time.
I find that thinking about who gets money when helps clarify things for me. The builder has gotten paid. He doesn't make any money by teaching you how to take care of your pool. Your builder has actually done far better than most. Quite a few will leave the chemistry wildly out of balance and vanish without teaching anything about actually caring for the pool. The pool stores make money when you come in and spend lots of money. When you are having problems is when they make money, so they are not motivated to help you solve your problems in any permanent way. There are some great builders and some great pool stores out there, but they are the exception rather than the rule.
On the other hand we are not here to make any money from you. We are here to help people out because were are passionate about pools and because we want to help save you from the mistakes that we have already made.
As I said, you don't really have to worry about anything but chlorine and PH for right now. Give it some time, read some more, and decide later.