I use 300yrds of Power Pro 30lb backing with 18lb leadcore. The purpose of backing is preventing being spooled by a large fish such as those on Lake Ontario and allows the paying out of all 10 colors.
I just take my leadcore reels to AJ's and he put backing, 10 colors of 18# leadcore and 100' of mono, cheaper then I can buy just the leadcore anywhere around here LOL Take Care God Bless LOL Dave