I had a pond on the farm where I grew up that gave me the same frustrations. It had floating islands of algae which kept the water crystal clear. I could watch the bass ignore everything in my box. Just like you described, I tried fast, slow, big, small, bright, dark, whatever!
Three things always worked in this pond:
1) The long black worm with white spots without a weight. I tried to keep it near the top of the water. I do not know where I got it, but my father told me it is supposed to mimic a baby snake, (and there were a lot of snakes there).
2) The silver Devils Horse. I worked it like a Rapala top water, a jerk just hard enough to get the props to spin for maybe a second, stop until all the rings in the water are almost gone. Then do the process all over again. For some reason the silver one is the only one that worked in this pond, but anything else silver did not work.
3) One time I found and caught a lizard and decided to use it as bait. I only did it once, but as soon as the bait hit the water, something grabbed it and my ten pound test line snapped. I never saw the fish, but I knew there were some huge ones in there, and it fought a little before the line broke, so it couldn't have been a turtle.
I always wanted to try the lizard thing again. I was just lucky enough back then to catch one to use as bait. Haven't caught one since.