Trying to catch Grass Carp on a fly rod is one of the most difficult things I have ever tried to do.
In college I found a pond right up the road from where I lived and I spent about a month straight going to this pond every afternoon trying to figure out how to catch one of these fish. There were only a couple of hours during the day where the sun was high enough in the sky that you could see into the water and sight fish for these 3 foot long behemoths. I would wade out about 50 feet into the center of the shallow end of this pond to stand in the blistering sun to see maybe 1 or 2 feeding fish over the course of several hours.
Day after day I would try to get the perfect cast on these feeding fish, I kept trying smaller and lighter flies so that they would be more subtle when they landed in the water, but time after time I would startle them either with my cast or the fish just wouldn't like how I stripped the fly. After I spent 15ish days going out there I finally put a cast 6 feet in front of where the fish was feeding. I managed to strip the fly directly under the tailing fish's' mouth and I kept thinking that if this fish doesn't eat my fly on this cast I am definitely going to snap my fly rod over my knee.
To my surprise this fish took my fly, but just kept cruising along like nothing had happened. When I set the hook the line got tight but the fish barely twitched. He didn't change course as the line kept getting tighter and tighter. As the fish kept swimming it started taking out line and after about 15 seconds it finally realized that it had been hooked and took off like a mac truck, pulling out more and more line. The fish eventually calmed down but no matter how much pressure I put on it the fish didn't seem to care. It turned around and I could see its face, the fish did one head shake and the fly popped out of its mouth. After this carp spit the hook I went home like a dog with his tail between his legs. The following week they started construction on the bridge next to this pond blocking access to the pond through the time that I graduated college and moved to a different city. I am still bitter about that day.