Are you using a grinder or multiplier? I'd use a heavier mainline on the rock and surf fishing..I like to fish with multiplier and 0.50 mono as mainline and I'll use a leader, 0.7 to 0.8mm in among the rocks, or livebaiting/sliding on the beach, just in case I hook a proper fish. I use like 0.45 or .40 as my sinker line so if I am stuck I can just bust that off, retie a sinker and carry on. This is what works for me..? I have no clue how many lb's/kg's the various monos that I use, I just use the diameters as reference..0.35 for bass leader, 0.35-0.40 for light tackle multiplier spinning, 0.45 as sinker line for leader or grunters or others in the lagoons, 0.50 as mainline for rock and surf ,0.55 for heavier rock and surf mainline or sliding livebaits and also for heavy spinning, 0.60-0.65 for mase @#$% fish-spinning, 0.65 for light tackle standup tuna and 0.80 for the 50w's proper tuna reels..what lb's the are???LOL no idea I just know how hard you can pull on each before they break, 0.55 and above I can pull as hard as I can with the bend of a rod and good knots and it should not break, i'm not that strong hahaha
The sinker weight/type must suit the conditions, the bait and the rig/line...I fish light tackle sometimes and then the rod can only cast a 3oz, and I'll be on the light 10size multiplier with 0.40 or grinder with 30-50lb braid on and a 0.60-0.7mm mono leader FG'd on the end, but if I cant make the sinker sit on the sand then I use a small 2oz or 3oz wire grapnel on that rig, or a weedeater cord grapnel in the rocks..or sometimes in among the rocks for gallies you want your sinker to wash around a little to find the fish, and then the fish pull you free, so a bottle sinker is used, or piece of chainlink, or sparkplug or for the same reason a pyramid on the sand so it can shift around..Hope that helps..