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The 2.5 is a little one, too small for crappie and perch IMO. micro noodles work great on them.
I can never hook them. I see a nice thick suspended line come in that I'm 99% sure is a crappie and I raise up to him and jig. He will slowly come up and suck it in, a miss almost every time. If I do make contact I feel him for a split second and he's gone. Now up to a 4mm and I've got him nearly every time. Personally, I think a #20 hook is too small for crappie... even the 3mm at #16 is too small IMO. 4mm at #14 is just big enough to get a good hookup percentage.