Hi, I did a conversion from baquacil to chlorine this Spring. My pool was a hot mess when I opened it, as it had a pink slime issue last Fall when I closed it. If I could do it over, I would have drained it. Instead, I schlepped to the pool store and asked them to please take all my money and help me. mistake. They had me put massive amounts of shock in it, which did kill the biguanide, and made pretty colors. But, when I was finally ready to start with chlorine, they had me use massive amounts of granular shock, literally over 400 pounds of it when all was said and done, as I could not keep a chlorine level up. With all that shock and pucks, my CYA went so high that chlorine was being lost daily. 2 weeks ago I found this awesome helpful bunch and I now am on a better path. I'm waiting for my pool store to call me and ask if everything is okay.
So, short answer - drain it, if you have a place to AND if you can, fill it yourself. I drained my pool down 2/3 this week to get my CYA down, not as horrible as I thought it would be, and made me wish I had just done that to convert it. It's not a perfect level (60 versus 110 though) and I know that I can manage that through the rest of our new england summer. Over the winter I'm sure my CYA will diminish.
I bought the T100 test kit and spinner for testing, very happy with it.