http://www.aquamaniacs.net/profiles/aquati...hygrophila.php3 can this plant just be planted in the gravel.. and left??? or do i need to periodically add fertilizer?

itrs a 10 gallon, and 1 betta... with java moss, lucky bamboo, hornwort and a aponogeton crispus... thanks:D

Hygro is pretty tough. For example, I gave a big handful to a friend who's tank crashed. They have no lighting (other than what comes in a window) and a big black shark and several plecos (90gallon). I figured that the fish would eat them or they'd die within a few days due to the little bit of light. Its been 6 months, and while they haven't grown much, its still alive and kicking.

The thing about hygro is it grows pretty fast if you give it what it wants. Its a great starter plant. Doesn't need a ton of light or nutrients, but you will need to prune it quite often if you do give it what it likes. I just pinch off the stems and replant what I pinched off, or pull out the bottom half and throw that away. Its a great plant for filling up a tank.

With just one betta in there, you might need ferts. A root fert tab could work if it's rooted in gravel.

will goldfish eat this plant?

Mine don't. I also like sunset hygro and hygro difformis (wysteria).
When leaves break off, they srout roots and you have a new plant.

I have six goldfish and one corydora, will this plant hurt the corydora or will the six gf hurt the plant?

There is always a chance that a bigger number of goldfish will munch down any plant eventually, although this particular one has been known to be "goldfish safe". It might be the taste isn't that appealing, or the leaves are too hard to digest. Remember, even if some goldfish do not touch the plant, there is always the exception. Just be prepared for the worst and enjoy it when the plant is still there the next day....
I don't see how the plant could hurt the cory. My corys never touch any plant at all...