really depends on their temperment...i have sucessfully kept a jardi and silver together for years. every now and then they do nip at each other. the silver is 5in. larger then the jardi.
I got a 18 to 20 inch silver together with a 12 inch jardini-
NOt too sure on how long they have been together but not too long in my tank-Only about a month now together without ne problems...But not to say that wont change....