Are there any types of floating plants (except for duckweed) that goldfish won't eat the roots off of? Are there any that just taste really bad or anything? Water lettuce didn't work, and I think he eats the duckweed whole. Maybe it's a dumb question, but I find that floating plants do the best in my goldie's tank...when they don't get the roots eaten off of course lol. The algae in his tank seems to out-compete just about everything else I've tried plant-wise, and the surface of the water is what gets the most sunlight during the day. I'm getting kind of annoyed with the algae because it's built up enough that he's hiding in it again, but I don't want to take away a big source of biological filtration with nothing there to fill the gap.

Water sprite (Ceratopteris) is a lovely floating plant, but I don't know if your goldie would eat the roots off, if that is what he likes to do It is not expensive, so it might be worth a try.

Here is a webpage with a picture
http://www.petfish.net/sprit.htm