Your vine very well may be causing the smell.
As far as discus growth, I'm honestly not sure but I know they don't grow THAT fast if you don't powerfeed them. However you'll have to do more water changes for longer if you don't.
I'll have to check the vine for some time. The water changes I don't mind as long as get the other tank before they stay small although some permanently small discuss wouldn't look that bad in my opinion.