Stocking issue of a 90g tank

[211303]

I have a 90g tank with the following habitants:
6x geophagus orange head tapajos
6x leopard cory
2x bn pleco
14x lemon tetra

I know the tank is pretty much fully stocked, but as you can see, most of my fish don't use the upper level of the tank, so I would want to add some mid-top dwellers.

I am considering 5-6 dension barb (in Hong Kong you can get tank bred specimen easily, about $5 for a 2'' one), but I heard they are fast swimmer.

Do you think I should add a group in my tank? Will their fast movement spook my other fish? Thanks in advance.

[absolutangel04]

I have limited experience with Denison's, so somebody else may have different advice. But, from what I have personally seen, I would doubt that they will generally swim much higher than the lemon tetras do. If you want some more filler in the upper regions, I would consider hatchets (make sure to have a good cover) or perhaps harlequin rasboras which seem to stay higher in the tank than many other schoolers.
Honestly though, if you really want Denison barbs, I would say go for it. They are wonderful fish and I really doubt that their movement would spook the geos. You can always trade them out for something else later if you decide the combo isn't quite right. In my opinion, there is nothing wrong with a bit of trial and error with getting a good mix as long as you can keep the parameters in check and you are not dealing with very aggressive fish that might damage each other. Also, so long as you are able to responsibly rehome the fish you need to remove.

[211303]

I end up getting a group of 13 emperor tetra, with 4 male and 9 female, as I decide the barbs are just not quite suitable for my tank. The tetras seem happy in the tank, and start eating in only an hour. However, since the emperor tetra are in the tank, the lemon tetras, which are originally in the tank and swim in tight formation, stop schooling and scatter around. The emperor tetra also didn't school. I know that fish would only school when they feel danger, but I don't understand why adding another species of fish will stop them from schooling. Does anyone have similar experience?