My story starts the same, but is different than everyone else. We also bought a house with a pool in the fall and the pool was closed when we moved in. In the spring the pool store that built the pool contacted us about opening and suggested I attend their free "pool school" if we wanted to maintain the pool ourselves. Knowing nothing of pools I went, where they explained the various chemicals, parts of the pool, etc. This is where my story gets different. They hammered in two things, you can't maintain a pool without a good test kit, and had lots of horror stories about copper and other side effects from random chemicals home owners have dumped in their pools, so I ended up leaving the store with one item, the only test kit they sold, the k-2006.
One part I remember clearly. Pool store: "You can't maintain a pool with test strips", some customer objected, so they changed their statement "You can maintain a pool for a while with test strips, when it turns green call us."
A month later we opened the pool to a CYA off the charts. The pool store warned me not to drain the vinyl liner down more than 8" and said I'll probably have to do it a few times. After 5 20% drain and fills and still above 100 CYA, I decided to start searching for alternatives. Also in their "pool school" they alluded to maintaining a pool with CYA higher than 50 but didn't recommend it, and mentioned their ranges for the other numbers were not valid in that case, so I decided to investigate what that was about and if anyone had a better way to lower CYA and found this site. I found out what the pool store taught me was mostly true, but I like the details from this site knowing why it works the way it does so much better.
So I'm not sure if the previous owner knew they were selling and decided to use up any remaining tri-chlor or if it was because it was a bad drought that summer, but without that high CYA I may have never gotten curious and found this site. I think the pool store method of our pool store matches close enough I may not have had any problems.
FYI I ended up lowering CYA by shutting down the pump and starting a siphon from the skimmer at the shallow end, and setting up a matching fill in the deep end. Since the fill water was still cold I think I minimized mixing and after 3 days of that 10,000 gallons later with almost no work I was down to 70 where I called it good to start the first year. In total 30,000 gallons to get my CYA I estimate was above 300 down to 70 for a 20,000 gal pool. Luckily water is cheap here.