May be the start of whirling disease? Do a search on the subject yahoo or the like, www.about.com has info. For some reason a link wont work. Go to the homepage and search under, home & garden, pets, freshwater fish. Have you given them any tubifex worms?

Feed them peeled peas. I take frozen organic, like maybe 10 or so, put them in some hot water to defrost them, peel the skins and then feed. See if this'll help. Might be just a digestion problem.

I haven't given them any tubifex worms, but they have been in the pond all summer and have eaten everything that fell in. They seem to be feasting on my hornwort in the aquarium, could this be a problem?
Should I take out my java fern? - will they munch it down to nothing?

Goldfish and koi pretty much will eat any plant. Do try the peas. It helps to clean out the digestive system. Unless you don't care about the java fern, consider it gone unless you remove it.

Peas work, if they dont eat that epsom salt added to the water will flush them out. Also saturate there food with a few drops of parafin or castor oil. I wonder if haveing "sacrificial" ( or sacrifishal) plants would work in a bigtime herbivore aquarium like a goldfish's. Keep the sturdy plants like java's for decor and raise a more plalatable plant or plants in a seperate tank and just drop them in for feasting. Worth a shot I guess.

All that's ever occurred when I've kept goldfish in tanks (as opposed to pond set up) is that the plants that have been ripped to pieces clog up the filter before long - and the water gets murkier than it's worth from the decaying plant parts. I can't even keep the fake plants (which are in the tank solely for decorative purposes of course) in the gravel since goldfish tend to root through the gravel and the plants go floating or topple sideways.

I'll feed the goldfish blanched greens, zucchini or peas, but other than that, I keep plants far away from them.