Generally, most geophagus are better served in groups. Both species in your list are too large to be kept this way in a 125. I'm not sure what your reasoining is behind geos producing less waste. All fish eat and poop. The more they eat the more they poop. The one advantage is that geos sift through the substrate, eating bits of otherwise wasted food. This would be a benifit in a tank with a messy oscar. There are some smaller geos that could work, but I would make sure they were grown out before adding an oscar.
Gymnogeophagus, usually need a few months of the year in cooler waters. The temperature would depend on the exact species, but would not be favorable to the other fish in your tank.
As for the eel and bicher, I would make sure they were well grown before adding an oscar.
Gymnogeophagus, usually need a few months of the year in cooler waters. The temperature would depend on the exact species, but would not be favorable to the other fish in your tank.
As for the eel and bicher, I would make sure they were well grown before adding an oscar.