Ok a few months ago I bought PLine thinking it was Fluorocarbon. (I haven’t used it yet being I just got my boat back) Anyway I just got some Berkley Vanish, knowing that it is Fluorocarbon. My questions are these 1) do I have to backfill my reels with mono?, 2) what test line should I use?    The Pline is 12lbs and Vanish is 14lbs. I still plan on using braid line but was just going to try Fluorocarbon, anyway thanks for your thoughts 

Pline floroclear is a decent line I have 15 pound spoooled up on my spinnerbait rod I like it I have also used 12 pound for square bills and crank baits. I have no experience with berkly line.

The Pline is okay, but not a line I liked personally even though I like most of their offerings. You might be able to use the Vanish to hang pictures or something, it'll probably still break doing that though. 

I don't like fluorocarbon... it's slippery, it cuts you when you try to pull knots tight, knots don't hold well even if they are tightened, it has tons of memory, jumps off of spinner reels, and is stiff as a board with little give to it; therefore, easily breaks. It's just a pita to me, I've seen no benefits whatsoever to using it. I've used the P-line fluoroclear for a while now, it's a good middle ground between mono and fluoro. It's basically mono encased in fluorocarbon, so a bit more neutrally buoyant whereas mono is bouyant and fluoro sinks. It can be used for most any situation really, mainline or leader. And it's strong and easy to cast and deal with. I only run it on my spinner reels atm though, so I am not sure in what scenario you'd need a backing on it. It seems to do fine held on with a 3-4 wrap pitzen knot for me, straight to the spool. I agree to stay away from the Vanish fluorocarbon... it just doesn't seem to be very good quality at all. They call it Vanish cause it'll make your rigs vanish, never to be seen again into the depths of Davy Jones locker. Go with Seaguar if you want to use fluorocarbon.