Hmm. Thanks for the suggestions. I'm fairly certain it's anchor worm, as the images on the internet look almost exactly the same.
The anti-parasite/ick medicine has Malachite Green -- as I said, I put in the normal dose. Hopefully this will clear up, but if not, I'll try some different...
I'm trying to get a 55 gallon community tank to go. I threw in some fairly large bait goldfish I got from a baitshop (yes, I know -- not the best of care), and I have left them in, and I'm planning on taking them out fairly soon. On 1 of these goldfish, I found something that looked like a...