I'm not sure if this has been done to death here but a few years ago I started to use Fluorocarbon because it seemed to be the way forward for nymphs etc and also it's supposed to have the same something or other as water (forgive me, it's an age thing but can't remember what it is) therefore its not as visible as nylon.
Most of the fish I was catching were about 1.5 - 3lb using Grand Max Soft Plus 15lb to 8.2lb joined with a blood knot a perfection loop and Trilene knot to the hook. Now this was fine until just before lockdown I gave one of these leaders to a friend and we were fishing at Rockbourne Trout Fishery Hampshire, where the fish are substantially larger. He hooked into a fish, possibly about 4-5lb, we managed to see it but it shot off and broke the line. Now he's a fair to middling fisherman and was playing it well with a medium rod, so I don't think he did anything wrong. We both changed to 8lb nylon and landed our fish averaging 5lbs.So I have stuck to Nylon/ Copolymer ever since.
This really annoyed me so I did some research and some tests, firstly on the Grand Max. The 8.2lb line broke at 2lbs at the blood knot, so thinking it was the knot tried others and couldn't get passed a Figure of Eight at 3.7lb. So I thought it was this particular line and therefore did some more tests.
I used Grand Max Plus, Whychwood Competition Fluoro, Scierra Fluoro and Cortland Ultra Premium Fluoro - and tested them against Hardy Copolymer, Drennan Supplex, Snowbee Premium Copolymer and some Drennan Specimen I had left over. I tied all the knots carefully making sure they didn't pinch, ranging from Figure of Eight, double FoE, 5 turn Grinner, Grinner loops, Perfection Loops (rubbish) Toit Knot, Kreh Loop, Rapala Loop etc.
The outcome was astonishing, Nylon/Copolymer trounced Fluoro. The Grand Max again didn't get passed 3.5lb and the other Fluorocarbon lines didn't get passed 70%, the Cortland 10.9lb only reaching 6.5lb at the most.
However the Copolymer/Nylon lines achieved at least 80% line strength and some like the Drennan Specimen 10lb broke at up to 13lb with all the same knots. Oh and one more thing, once the Flouro had been tightened, it's strength almost halved again, whereas the nylon lines retained most of the original strength.
Of course rods play a good part in cushioning the line, but this opened my eyes to adverts suggesting some Fluoro line were 100% at the knots.
Sorry about all this blurb and I hope you didn't fall asleep but after all that I would like to know if anyone knows of a Fluoro line with actual good knot strength? Or at least another knot I could use if there is one I've missed?