I would just keep the fish you have, chances are they are way more entertaining than a bichir, I have a senegal that just swims aimlessly around the tank and it gets annoying to look at, graceful fish that have personality such as your texas are keepers.
The absolute minimum size tank you should keep a senegal in is a standard 30 gallon tank.The general guide is the tank should be 3-4 x the lenght of the fish being kept and 1 1/2 times as wide. but hey its your fish -Anne