i keep uaru fernandies and a uaru amp in with my RTG with no problems at all i even have a 4.5'' geo in there for a few months and have had some 2-3'' cory's for a couple of weeks although these are going when i go to the lfs next.
Jardinis grow at a much slower rate than Silvers, and I think they max out at 18-24" vs. 24-36" for Silvers. Also, Jardinis tend to utilize more levels of the aquarium (top and middle) vs. Silvers which just tend to stay at the top level. Hence, I think you can get away with a smaller volume tank (125 gal) with a Jardini vs. Silvers (180 gal and up).