I haven't planted the goldfish tank as yet, so I don't have a heck of a lot to contribute
However I do have herb fish in a heavy planted tank.
The problem with goldfish is that they not only eat plants, but they dig as well.
You can try anubias, crinum (onion) and green melon (not red, herb fish will eat red). What you need to do is make sure you have fairly large rocks around the roots of the plants so that the goldies cannot dig them up. You can try the anubias on wood or rock, but make sure you tie it really tight or they could rip them off.
Try to plant mature plants, not young ones. The young ones taste better and they'll be more apt to munch on those. As it is they may remove the new leaves and/or nibble on the outside edges of the old ones. Depends on the individual fish.
Plant some water sprite and anacharis for them to nibble on and they may leave the rest of the plants alone.
Hope that helps
Oh, in regards to the comet with the fancies -- it's not just the food competition between the two that is the problem, comets have been known to attack fancy goldfish and rip their fins off. You may not have a problem with the size tank you have, however comets will get too big even for a 75g. Keep an eye on them for aggression or you could lose the fancies.
Roan
