You can't drain 80% of a liner pool, in most cases. There is a way to replace the water in a vinyl pool without draining it, but it's a PITA.

Do this:

1. Get the Taylor K2006 kit. You'll need it, no matter which direction you go. http://pool9.net/tk/

2. Fill out the pool equipment form, so I have a clear picture of what you're dealing with: http://pool9.net/pf-equip-form/

3. Continue to use the Nature2 (copper) and bromine, till you have a COMPLETE plan for conversion. You do not want to have the pool turn green while you work things out!