SDs will completely destroy live plants otherwise I would have considered them.
It`s not necasarilly to stop them from fighting, but more to create some movement in the open water column, the tank looks pretty empty at times, the geos are all playing very nicely together with the Tapajós redheads at the top of the food chain.
I was thinking Giant danios or Panda barbs maybe, The only reason I decide not to go with black skirts is because I have used them as my go to group of open water fish for the last few years, they are usually the first fish I will add to a tank when it is stable.