Skimming through one such post:
Feed them daily with salad/plant based foods. Kale seems to be a favorite. Dandelion and beet greens.
Ludwigia Repens
Cryptocoryne Crispatula var. Balansae
Red jungle Val
Corkscrew val
Amazon sword
Cryptocoryne Wendtii Green
Water sprite
Cryptocoryne Retrospiralis
Dwarf Sag
Pennywort
Vals- but keep feeding plenty of vegetables or else these may get eaten.
Maybe any of several Swords
NOT Java Moss or Subwassertang
Maybe Pennywort- nibbled, but fast grower vs. gets uprooted.
NOT frogbit (I do not know which species they were talking about)
Crypts
Wisteris gets nipped a bit, but grows fast.
Sag gets nibbled, but only when they lack other salad.
Hornwort can get bitten, not sure if they eat it.
There is a lot more to this thread:
http://www.plantedtank.net/forums/showthread.php?t=156649&highlight=goldfish
Bump: A thin white worm, most are detritus eaters, and most fish will eat the worms.