Off topic, but why would anyone keep goldfish? They are hideous. Hideous caricatures of selective breeding, I mean. With their short bodies, googly eyes (my scientific term), gelatinous bags under their eyes, weird red cap thingy, errrrr. They are messy and annoying. I despise goldfish.
On another note, I believe anacharis is the old standard for goldfish tanks. Easy, hardy, likes low temps, etc. Personally I don't like the look of anacharis, so if I for whatever reason had a goldfish tank I'd do E. najas. Just as easy, and looks much better.
Ok, someone here will debate my loathing for selectively bred fish. Okay, fine, I do keep some animals that are selectively bred. Cherry shrimp, halfmoon plakat betta, A few snakeskin guppies. Fine, but those do not deviate nearly as much from the original animal as much as goldfish do. Has anyone here seen a carp? You look at a carp and a Ryukin goldfish and then dispute me.
Sorry for the rant, Milalic. I had that one brewing for a while. Also, I was thinking you might like L. sessiflora. My favorite plant, I recommend it for every setup. Fast growing, super simple, and even though it won't put up with a goldfish's foraging, it will grow back so quickly you will hardly notice. Also, it loves all light levels.