I was wondering how long it would take for a sliver to outgrow a 135 that is 18in deep. Could it be house with 1 or 2 large cichlids like GT and JD? The tank is cycling and it is filtered by a 20gal wet/dry sump.
As long as the aro is at least twice the length of something like an oscar or JD you'll be fine. A 6 inch oscar isn't going to bash up a foot long silver.
But if you're concerned, just get a jardini instead