I purchased some FC Sniper and InvizX for my spinning and baitcasting reels, respectively. Should I use backing, and if so, how many yards?

I don't think you need backing for flouro, But, if you're like me, you like to save money. I use some elcheapo backing line on all of my reels. I use the same diameter, or as close as I can get.

Fill your reel all the way with the cheap stuff. Now tie on a weight the same weight as you plan on using with that rig, or maybe just a little bit more. Make a long cast, as long as you can. Now tie a knot in the line to mark the spot, and crank it back in. Remove the elcheapo line down to the knot and strip off just a bit more before you cut it. Now tie on your good line, and fill it up.

You'll only have to do this the first time, From there on out, you just strip it down to the knot, cut and tie, and refill it.

A bck-to-back uni knot makes a good connection, but a blood knot will work.

Cheers,

GK

I do the same as ghoti.  Not because its needed because the line is so expensive.  

I just fill the reel with cheap stuff about 1/2 way though.

I use backing on all my reels and spool on about 60 yards of the line I'm actually fishing with.

I take off pulls so 35 pulls is 105 ft. All my reels are done this way so I get the knots at the same time.

Garnet

I do the same as ghoti. Not because its needed because the line is so expensive.

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I do the same too.