Fussy is more of a human thing. Fish eat when considtions and food is right.

Fish do sometimes need to be taught to come to the surface to take floating food, but once they know about that, which I assume they do from the flake, they should be fine with floating pellets. You could try grinding up some pellets and trying that, or flake food plus pellets assuming floating pellets. If they pick the flake out and ignore the pellets I'd say there's a problem with the food. If they're taking in pellets and spitting them out the food is bad.

If all the fish aren't eating anything the problem is probably with water quality.

Bumps on fish can be many things. Parasites under the skin. tumors, bacteria, virus. Step one is always to figure out which. However, I'm in the same boat as the other poster, have never cured a fish. I stopped trying years ago. Dealing with parasites in the pond OK. Treating new fish as a precaution OK. Making sure water quality is good so their immune system is good, OK. But actually curing a specific problem with a fish, I don't even try any more.

thanks for the comments waterbug_guy......well the pellets are only 2mm in size, much smaller than when I tried it a few years ago & I was hoping this would be the problem why they didn't take them then. The water quality hasn't changed in one day (between feeds) & it's crystal clear as I have an extensive filter system encompassing mechanical, bio & uv sytems. The water circulates through & is cleaned about 5 times a day! The few fish that have had a nibble at the pellets aren't spitting them out but that's a good point & thankyou for pointing it out. I probably will get some more flakes & intermingle the food darn them! But I really do love them :-) Cheers....largo

You might try pre soaking the pellets in water before feeding. Some pellets can be quite hard and my fishies at least have tender mouths.

If the food was improperly stored, it could have become rancid.

Hope you'll update later. It's an interesting problem.

What are your water parameters? Ammonia, nitrite, nitrate, pH, gh, kh? I also wonder about a water quality issue.

I currently have 90 koi cohabitating w/ goldfish and golden orfe with zero signs of aggressiveness. That's odd behavior, as they are highly social and gentle fish. I've only seen them "pick" at other fish when they have open wounds and it seems like a snack bar to their senses. lol

Any chance of a photo of these bumps/wounds/whatever they are?

As for treating fish for individual issues, I've had great success and will gladly share what I've learned! :)

ademink, your advice is above my pay grade, clearly U r an expert Koi wrangler. I do have a water testing kit but being colour blind myself it is useless to me! I am fairly sure the water is good tho as I previously said they ate flakes one day & not pellets the next & they have refused pellets last time I tried as well. The water wouldn't have changed much in one day. My pellet supplier suggested I mix pellets & flakes & over time reduce the flakes. This sounds sensible. What do U think? Yes the Koi r gentle giants. The few fish (about 3 out of 25) that have bumps are ok until as you say a wound appears then it's pick pick pick. Also I found that I catching a sick fish is easy 1st time but they learn & soon dart under cover so I gave up trying. The urban myth that fish have short memories is just that! A myth! I agree they are not aggressive but if one of the smaller breeds swims past the bosses, (2 big Koi) they will lazily bite their tails off! (Just to remind them who's in charge lol)