Val (several species) and Hornwort are the ones that thrive in my hard water tanks. GH and KH are roughly the same in my tanks. My hard water tanks have GH and KH between 8-10 degrees.
Duckweed does well in every tank except one (I think the fish eat it). Water Lettuce overran one of my hard water tanks, and I was thinning it often. Bolbitis was growing well in that tank too.

 

I think all the anuibia should be pretty good in that high gh...

 

From my experience, it's not the high gh that will limit certain plants, it's high kh. GH measures Ca and Mg levels, kh measures amount of carbonates in the water. I would suggest figuring out if your high gh is a result of too much Ca, too much Mg or of both. If one is much higher than the other, you might want to dose the lower one (ratio of 4:1 Ca:Mg, roughly). If your kh is under 6, and all other conditions are fine, you can probably grow most anything except the real soft water types, ie, Erios, Toninas. With a kh of 10 and gh of 12-13, I have grown a fairly large number of plants without issues.

 

i haven't tested kh lately, but from what i remembered it was 8 or 10 and the 25gh was a month after a water change so i don't know what it was when i first put the water in the tank (i'm assuming it must've gone down). i haven't tested calcium in my water yet. when you say if kh is under 6 and all other conditions fine.... so what happens then when the kh is higher with all the other conditions fine?