Agree with the rest, probably best not to introduce any tank mates which swim in the middle/ top. Even at the bottom, it's a bit of a risk because apparently jardinis feed from all levels of the tank..? Something I've heard, but maybe someone can confirm this? Especially since the jardini's already in the tank, adding new tank mates would be intruding on HIS territory now, so they're going to suffer. Plecos should be OK, but mine gets its fins nipped by my green all the time. Would advise against an oscar, even though many people/ logic would say that it's possible. I got one recently and had to remove him after a few days - he was so badly beaten up. The aro basically forced him to stay in a corner of the tank and wouldn't let him come to the middle/ top. Now I've got an excuse for a second tank! :happy2:
..but yeah, jardinis are known to be cra-zyyyy, so just be careful.