Hello Row,
I have some similar issues. I have 2 loaches, 1 caramel pleco, 3 otos, and 2 catfish sharks hanging out in my 30g tank, so i needed to get more fish towards the top of the tank. So I bought 4 serpea tetra's, and two gold barbs ( i had barbs 4 but 2 died when i had a very quick moving ich problem :'( ). The barbs will go and eat where ever they can get food but will hang out in the middle of the tank when not eating. They dont go to the top at all.
But the serpea's and the barbs are both nippy fish, so they get along with each other (for the most part lol). But dont expect them to hang out at the top. The one thing my girlfriend and myself have noticed is that these fish mimic other fish. Where they hide, where they swim and stuff. Beacuse some days they are out and having a good time, and other days they are hidding with my loachs as soon as someone passes the tank.
So I hope that helps you out a lil. Good luck, don't forget the pics!!