I had 7 Buenos Aires Tetras with my Midas, over the course of a month it was down to 4. My Midas is not that aggressive or large yet, but the tetras were always nipping on each others fins and he would end up taking out any that could not swim away fast enough. This all happened in my 65g growout so there was really no where for the tetras to run. In a 125g thats 6' long the larger type tetras should be fine, just expect a few to go missing every now and then.
